| 0/0 |
2026/01/09 20:42 |
flow |
assessment-kcsan |
2m
Model:
Results: map[Benign:true Explanation:The data race is benign.
The KCSAN report indicates a data race in `usbdev_ioctl` -> `usbdev_do_ioctl` -> `inode_set_atime_to_ts`. The race occurs on the `inode->i_atime_nsec` field (based on the 4-byte write size and the context of timestamp update).
Analysis of the code in `drivers/usb/core/devio.c` reveals that `usbdev_do_ioctl` updates the inode's access time (`atime`) after processing the ioctl command:
```c
2816: if (ret >= 0)
2817: inode_set_atime_to_ts(inode, current_time(inode));
```
The `inode_set_atime_to_ts` function in `include/linux/fs.h` performs a direct write to the inode's timestamp fields:
```c
1621: {
1622: inode->i_atime_sec = ts.tv_sec;
1623: inode->i_atime_nsec = ts.tv_nsec;
1624: return ts;
1625: }
```
The write to `i_atime_nsec` (likely `u32` or similar 4-byte integer in `struct inode`) corresponds to the reported 4-byte data race.
While the ioctl processing itself is protected by `usb_lock_device(dev)` (lines 2610-2815), the `atime` update happens *after* the lock is released (line 2815). Consequently, if multiple threads perform ioctls on the same USB device file concurrently, they may race to update the `atime`.
This race is considered benign because:
1. **Nature of Data**: The race is on a timestamp field (`atime`). `atime` updates are generally considered metadata updates where strict serialization is not critical for system stability or security. The worst-case outcome is that the `atime` reflects the time of one of the concurrent calls, or a mix of seconds/nanoseconds from close timestamps, which is acceptable for `atime`.
2. **Atomicity**: The write is to a primitive integer type (4 bytes), which is atomic on the x86_64 architecture. There is no risk of storing a corrupted value (other than "lost update").
3. **No Logic Dependency**: The kernel logic does not rely on strict ordering or atomicity of `atime` updates in this path for correctness or memory safety.
Therefore, this is a harmless race on a statistics/metadata field.]
|
| 1/1 |
2026/01/09 20:42 |
action |
kernel-checkouter |
0m
Model:
Results: map[KernelSrc:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/761c89d80a8577d5dba2a721de12cc04cb43ff14]
|
| 2/1 |
2026/01/09 20:42 |
action |
kernel-builder |
0m
Model:
Results: map[KernelObj:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/9dce9dd65e825296b412dc760805ab08dc7d0dbc]
|
| 3/1 |
2026/01/09 20:42 |
action |
codesearch-prepare |
0m
Model:
Results: map[Index:codesearch-index]
|
| 4/1 |
2026/01/09 20:42 |
agent |
expert |
2m
Model:
Results:
Instruction:
You are an experienced Linux kernel developer tasked with determining if the given kernel
data race is benign or not. The data race report is from KCSAN tool.
It contains 2 stack traces of the memory accesses that constitute a data race.
The report would be non-actionable, if the underlysing data race is "benign".
That is, the race is on a simple int/bool or similar field, and the accesses
are not supposed to be protected by any mutual exclusion primitives.
Common examples of such "benign" data races are accesses to various flags fields,
statistics counters, and similar.
An actionable race is "harmful", that is can lead to corruption/crash even with
a conservative compiler that compiles memory accesses to primitive types
effectively as atomic. A common example of a "harmful" data races is race on
a complex container (list/hashmap/etc), where accesses are supposed to be protected
by a mutual exclusion primitive.
In the final reply explain why you think the report is consistent and the data race is harmful.
Use the provided tools to confirm any assumptions, what variables/fields being accessed, etc.
In particular, don't make assumptions about the kernel source code,
use codesearch tools to read the actual source code.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The data race report is:
==================================================================
BUG: KCSAN: data-race in usbdev_ioctl / usbdev_ioctl
write to 0xffff8881021a3540 of 4 bytes by task 15000 on cpu 0:
inode_set_atime_to_ts include/linux/fs.h:1624 [inline]
usbdev_do_ioctl drivers/usb/core/devio.c:2818 [inline]
usbdev_ioctl+0x5f3/0x1700 drivers/usb/core/devio.c:2827
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
write to 0xffff8881021a3540 of 4 bytes by task 15007 on cpu 1:
inode_set_atime_to_ts include/linux/fs.h:1624 [inline]
usbdev_do_ioctl drivers/usb/core/devio.c:2818 [inline]
usbdev_ioctl+0x5f3/0x1700 drivers/usb/core/devio.c:2827
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
value changed: 0x388bef8e -> 0x3b86e00e
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15007 Comm: syz.3.4166 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================
Reply: The data race is benign.
The KCSAN report indicates a data race in `usbdev_ioctl` -> `usbdev_do_ioctl` -> `inode_set_atime_to_ts`. The race occurs on the `inode->i_atime_nsec` field (based on the 4-byte write size and the context of timestamp update).
Analysis of the code in `drivers/usb/core/devio.c` reveals that `usbdev_do_ioctl` updates the inode's access time (`atime`) after processing the ioctl command:
```c
2816: if (ret >= 0)
2817: inode_set_atime_to_ts(inode, current_time(inode));
```
The `inode_set_atime_to_ts` function in `include/linux/fs.h` performs a direct write to the inode's timestamp fields:
```c
1621: {
1622: inode->i_atime_sec = ts.tv_sec;
1623: inode->i_atime_nsec = ts.tv_nsec;
1624: return ts;
1625: }
```
The write to `i_atime_nsec` (likely `u32` or similar 4-byte integer in `struct inode`) corresponds to the reported 4-byte data race.
While the ioctl processing itself is protected by `usb_lock_device(dev)` (lines 2610-2815), the `atime` update happens *after* the lock is released (line 2815). Consequently, if multiple threads perform ioctls on the same USB device file concurrently, they may race to update the `atime`.
This race is considered benign because:
1. **Nature of Data**: The race is on a timestamp field (`atime`). `atime` updates are generally considered metadata updates where strict serialization is not critical for system stability or security. The worst-case outcome is that the `atime` reflects the time of one of the concurrent calls, or a mix of seconds/nanoseconds from close timestamps, which is acceptable for `atime`.
2. **Atomicity**: The write is to a primitive integer type (4 bytes), which is atomic on the x86_64 architecture. There is no risk of storing a corrupted value (other than "lost update").
3. **No Logic Dependency**: The kernel logic does not rely on strict ordering or atomicity of `atime` updates in this path for correctness or memory safety.
Therefore, this is a harmless race on a statistics/metadata field.
|
| 5/2 |
2026/01/09 20:42 |
llm |
expert |
0m
Model:
Thoughts: **Analyzing a KCSAN Data Race in `usbdev_ioctl`**
Okay, so I've got this KCSAN report, and it's pointing at a data race within `usbdev_ioctl`. The report says the race is happening on address `0xffff8881021a3540`, and both accesses are 4-byte writes. The stack trace is pretty illuminating: it shows the critical call chain is `inode_set_atime_to_ts` within `usbdev_do_ioctl`, which is then invoked by `usbdev_ioctl`.
My initial thought is that `inode_set_atime_to_ts` is likely the culprit, as it's the function writing to the shared address. This usually means we're dealing with a race related to updating the access time of an inode. I need to confirm this, though.
First, I need to see *where* in the code this is happening. Let's start by looking at the source code. I should probably check `drivers/usb/core/devio.c` around lines 2818 and 2827 to see the call context for `inode_set_atime_to_ts` and what it's operating on. It's always good to refresh my memory and double-check, so perhaps a quick listing of entities in `drivers/usb/core/devio.c` wouldn't hurt.
Actually, scratch that β the `codesearch-definition-source` tool is probably the better way to do this; it'll give me a more accurate picture of the surrounding code. I will start there, and read the definitions for both `usbdev_do_ioctl` and `usbdev_ioctl`. I want to understand the exact flow and context of this race, so starting with `usbdev_ioctl` in `drivers/usb/core/devio.c` is the right place to begin.
|
| 6/2 |
2026/01/09 20:42 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:usbdev_ioctl SourceFile:drivers/usb/core/devio.c]
Results: map[Missing:false SourceCode:2821: static long usbdev_ioctl(struct file *file, unsigned int cmd,
2822: unsigned long arg)
2823: {
2824: int ret;
2825:
2826: ret = usbdev_do_ioctl(file, cmd, (void __user *)arg);
2827:
2828: return ret;
2829: }
SourceFile:drivers/usb/core/devio.c]
|
| 7/2 |
2026/01/09 20:42 |
llm |
expert |
0m
Model:
Thoughts: Here's the summary:
**Digging into the USB Device I/O Control Flow**
Alright, I'm tracing through this `usbdev_ioctl` function call, and it's pretty straightforward β it seems to just be a wrapper that delegates to `usbdev_do_ioctl`. I need to figure out what's going on underneath, so I checked the stack trace. That's where I see `usbdev_do_ioctl` is calling `inode_set_atime_to_ts`. That's interesting; it's touching file access times. Let's get to the bottom of this. Time to locate `usbdev_do_ioctl` within the driver code. I'll open up `drivers/usb/core/devio.c` and see what's actually going on. Hopefully, the surrounding code in that file will provide some context and clue me in to why that `inode_set_atime_to_ts` call is happening.
|
| 8/2 |
2026/01/09 20:43 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:usbdev_do_ioctl SourceFile:drivers/usb/core/devio.c]
Results: map[Missing:false SourceCode:2594: /*
2595: * NOTE: All requests here that have interface numbers as parameters
2596: * are assuming that somehow the configuration has been prevented from
2597: * changing. But there's no mechanism to ensure that...
2598: */
2599: static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
2600: void __user *p)
2601: {
2602: struct usb_dev_state *ps = file->private_data;
2603: struct inode *inode = file_inode(file);
2604: struct usb_device *dev = ps->dev;
2605: int ret = -ENOTTY;
2606:
2607: if (!(file->f_mode & FMODE_WRITE))
2608: return -EPERM;
2609:
2610: usb_lock_device(dev);
2611:
2612: /* Reap operations are allowed even after disconnection */
2613: switch (cmd) {
2614: case USBDEVFS_REAPURB:
2615: snoop(&dev->dev, "%s: REAPURB\n", __func__);
2616: ret = proc_reapurb(ps, p);
2617: goto done;
2618:
2619: case USBDEVFS_REAPURBNDELAY:
2620: snoop(&dev->dev, "%s: REAPURBNDELAY\n", __func__);
2621: ret = proc_reapurbnonblock(ps, p);
2622: goto done;
2623:
2624: #ifdef CONFIG_COMPAT
2625: case USBDEVFS_REAPURB32:
2626: snoop(&dev->dev, "%s: REAPURB32\n", __func__);
2627: ret = proc_reapurb_compat(ps, p);
2628: goto done;
2629:
2630: case USBDEVFS_REAPURBNDELAY32:
2631: snoop(&dev->dev, "%s: REAPURBNDELAY32\n", __func__);
2632: ret = proc_reapurbnonblock_compat(ps, p);
2633: goto done;
2634: #endif
2635: }
2636:
2637: if (!connected(ps)) {
2638: usb_unlock_device(dev);
2639: return -ENODEV;
2640: }
2641:
2642: switch (cmd) {
2643: case USBDEVFS_CONTROL:
2644: snoop(&dev->dev, "%s: CONTROL\n", __func__);
2645: ret = proc_control(ps, p);
2646: if (ret >= 0)
2647: inode_set_mtime_to_ts(inode,
2648: inode_set_ctime_current(inode));
2649: break;
2650:
2651: case USBDEVFS_BULK:
2652: snoop(&dev->dev, "%s: BULK\n", __func__);
2653: ret = proc_bulk(ps, p);
2654: if (ret >= 0)
2655: inode_set_mtime_to_ts(inode,
2656: inode_set_ctime_current(inode));
2657: break;
2658:
2659: case USBDEVFS_RESETEP:
2660: snoop(&dev->dev, "%s: RESETEP\n", __func__);
2661: ret = proc_resetep(ps, p);
2662: if (ret >= 0)
2663: inode_set_mtime_to_ts(inode,
2664: inode_set_ctime_current(inode));
2665: break;
2666:
2667: case USBDEVFS_RESET:
2668: snoop(&dev->dev, "%s: RESET\n", __func__);
2669: ret = proc_resetdevice(ps);
2670: break;
2671:
2672: case USBDEVFS_CLEAR_HALT:
2673: snoop(&dev->dev, "%s: CLEAR_HALT\n", __func__);
2674: ret = proc_clearhalt(ps, p);
2675: if (ret >= 0)
2676: inode_set_mtime_to_ts(inode,
2677: inode_set_ctime_current(inode));
2678: break;
2679:
2680: case USBDEVFS_GETDRIVER:
2681: snoop(&dev->dev, "%s: GETDRIVER\n", __func__);
2682: ret = proc_getdriver(ps, p);
2683: break;
2684:
2685: case USBDEVFS_CONNECTINFO:
2686: snoop(&dev->dev, "%s: CONNECTINFO\n", __func__);
2687: ret = proc_connectinfo(ps, p);
2688: break;
2689:
2690: case USBDEVFS_SETINTERFACE:
2691: snoop(&dev->dev, "%s: SETINTERFACE\n", __func__);
2692: ret = proc_setintf(ps, p);
2693: break;
2694:
2695: case USBDEVFS_SETCONFIGURATION:
2696: snoop(&dev->dev, "%s: SETCONFIGURATION\n", __func__);
2697: ret = proc_setconfig(ps, p);
2698: break;
2699:
2700: case USBDEVFS_SUBMITURB:
2701: snoop(&dev->dev, "%s: SUBMITURB\n", __func__);
2702: ret = proc_submiturb(ps, p);
2703: if (ret >= 0)
2704: inode_set_mtime_to_ts(inode,
2705: inode_set_ctime_current(inode));
2706: break;
2707:
2708: #ifdef CONFIG_COMPAT
2709: case USBDEVFS_CONTROL32:
2710: snoop(&dev->dev, "%s: CONTROL32\n", __func__);
2711: ret = proc_control_compat(ps, p);
2712: if (ret >= 0)
2713: inode_set_mtime_to_ts(inode,
2714: inode_set_ctime_current(inode));
2715: break;
2716:
2717: case USBDEVFS_BULK32:
2718: snoop(&dev->dev, "%s: BULK32\n", __func__);
2719: ret = proc_bulk_compat(ps, p);
2720: if (ret >= 0)
2721: inode_set_mtime_to_ts(inode,
2722: inode_set_ctime_current(inode));
2723: break;
2724:
2725: case USBDEVFS_DISCSIGNAL32:
2726: snoop(&dev->dev, "%s: DISCSIGNAL32\n", __func__);
2727: ret = proc_disconnectsignal_compat(ps, p);
2728: break;
2729:
2730: case USBDEVFS_SUBMITURB32:
2731: snoop(&dev->dev, "%s: SUBMITURB32\n", __func__);
2732: ret = proc_submiturb_compat(ps, p);
2733: if (ret >= 0)
2734: inode_set_mtime_to_ts(inode,
2735: inode_set_ctime_current(inode));
2736: break;
2737:
2738: case USBDEVFS_IOCTL32:
2739: snoop(&dev->dev, "%s: IOCTL32\n", __func__);
2740: ret = proc_ioctl_compat(ps, ptr_to_compat(p));
2741: break;
2742: #endif
2743:
2744: case USBDEVFS_DISCARDURB:
2745: snoop(&dev->dev, "%s: DISCARDURB %px\n", __func__, p);
2746: ret = proc_unlinkurb(ps, p);
2747: break;
2748:
2749: case USBDEVFS_DISCSIGNAL:
2750: snoop(&dev->dev, "%s: DISCSIGNAL\n", __func__);
2751: ret = proc_disconnectsignal(ps, p);
2752: break;
2753:
2754: case USBDEVFS_CLAIMINTERFACE:
2755: snoop(&dev->dev, "%s: CLAIMINTERFACE\n", __func__);
2756: ret = proc_claiminterface(ps, p);
2757: break;
2758:
2759: case USBDEVFS_RELEASEINTERFACE:
2760: snoop(&dev->dev, "%s: RELEASEINTERFACE\n", __func__);
2761: ret = proc_releaseinterface(ps, p);
2762: break;
2763:
2764: case USBDEVFS_IOCTL:
2765: snoop(&dev->dev, "%s: IOCTL\n", __func__);
2766: ret = proc_ioctl_default(ps, p);
2767: break;
2768:
2769: case USBDEVFS_CLAIM_PORT:
2770: snoop(&dev->dev, "%s: CLAIM_PORT\n", __func__);
2771: ret = proc_claim_port(ps, p);
2772: break;
2773:
2774: case USBDEVFS_RELEASE_PORT:
2775: snoop(&dev->dev, "%s: RELEASE_PORT\n", __func__);
2776: ret = proc_release_port(ps, p);
2777: break;
2778: case USBDEVFS_GET_CAPABILITIES:
2779: ret = proc_get_capabilities(ps, p);
2780: break;
2781: case USBDEVFS_DISCONNECT_CLAIM:
2782: ret = proc_disconnect_claim(ps, p);
2783: break;
2784: case USBDEVFS_ALLOC_STREAMS:
2785: ret = proc_alloc_streams(ps, p);
2786: break;
2787: case USBDEVFS_FREE_STREAMS:
2788: ret = proc_free_streams(ps, p);
2789: break;
2790: case USBDEVFS_DROP_PRIVILEGES:
2791: ret = proc_drop_privileges(ps, p);
2792: break;
2793: case USBDEVFS_GET_SPEED:
2794: ret = ps->dev->speed;
2795: break;
2796: case USBDEVFS_FORBID_SUSPEND:
2797: ret = proc_forbid_suspend(ps);
2798: break;
2799: case USBDEVFS_ALLOW_SUSPEND:
2800: ret = proc_allow_suspend(ps);
2801: break;
2802: case USBDEVFS_WAIT_FOR_RESUME:
2803: ret = proc_wait_for_resume(ps);
2804: break;
2805: }
2806:
2807: /* Handle variable-length commands */
2808: switch (cmd & ~IOCSIZE_MASK) {
2809: case USBDEVFS_CONNINFO_EX(0):
2810: ret = proc_conninfo_ex(ps, p, _IOC_SIZE(cmd));
2811: break;
2812: }
2813:
2814: done:
2815: usb_unlock_device(dev);
2816: if (ret >= 0)
2817: inode_set_atime_to_ts(inode, current_time(inode));
2818: return ret;
2819: }
SourceFile:drivers/usb/core/devio.c]
|
| 9/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: **Decoding the USB Device IOCTL Access Time Update**
Okay, so I'm looking at this report and trying to make sense of the reported line numbers. Line 2817... that corresponds to `inode_set_atime_to_ts(inode, current_time(inode))`. But the report mentions `usbdev_do_ioctl` at line 2818, then `usbdev_ioctl` at 2827. In *my* disassembly, `usbdev_do_ioctl` ends at 2818 with the return statement. So the call to `inode_set_atime_to_ts` is *indeed* at line 2817. That checks out.
Let me just quickly confirm by looking at the C code. Yep:
```c
2816: if (ret >= 0)
2817: inode_set_atime_to_ts(inode, current_time(inode));
2818: return ret;
```
Ah, right. This is updating the access time of the inode. The `inode` is obtained via `file_inode(file)`, meaning it's the inode associated with the file descriptor used in the `ioctl` call. The critical part is the potential data race: `inode_set_atime_to_ts`. It's pretty clear: we have two threads calling `usbdev_ioctl` on the *same* file descriptor, or at least file descriptors pointing to the same inode. Both threads are going to be trying to update `atime` simultaneously. Time to delve into the `inode_set_atime_to_ts` implementation. I'll check `include/linux/fs.h` to refresh myself on the locking around that function.
|
| 10/2 |
2026/01/09 20:43 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:inode_set_atime_to_ts SourceFile:include/linux/fs.h]
Results: map[Missing:false SourceCode:1619: static inline struct timespec64 inode_set_atime_to_ts(struct inode *inode,
1620: struct timespec64 ts)
1621: {
1622: inode->i_atime_sec = ts.tv_sec;
1623: inode->i_atime_nsec = ts.tv_nsec;
1624: return ts;
1625: }
SourceFile:include/linux/fs.h]
|
| 11/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: **Deconstructing a Potential Data Corruption**
Okay, so I'm looking at this snippet of C code and a report that mentions a 4-byte write. The function `inode_set_atime_to_ts` looks like it's setting the access time for an inode, and I'm immediately noticing something that doesn't quite add up. The code snippet sets `i_atime_sec` and `i_atime_nsec`. I'm pretty sure `i_atime_sec` is a `time64_t`, which, on a 64-bit architecture, is an 8-byte `long long`. And `i_atime_nsec`... I need to double-check this, but it seems like it's a `long`, which is *also* likely 8 bytes on a 64-bit system. So, we are writing to two variables, each 8 bytes, totaling 16 bytes. But the report claims only a 4-byte write. That doesn't make any sense. There could be an issue with a race condition, or a concurrency problem, but first I need to ensure that my assumption about the sizes of `i_atime_sec` and `i_atime_nsec` is correct, and I'm going to do that by looking at the `struct inode` definition in `include/linux/fs.h`. That's where the definitive answer lies.
|
| 12/2 |
2026/01/09 20:43 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:inode SourceFile:include/linux/fs.h]
Results: map[Missing:true SourceCode: SourceFile:]
|
| 13/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: **My Search for the `struct inode` Definition**
Okay, so I need to find the definition of `struct inode`. Naturally, my first instinct is to check the standard include files within the Linux kernel source. Given that `inode` is fundamentally tied to the file system structure, I'm confident it will reside within the `include/linux/` directory, specifically in a file related to the file system layer. I'll start by looking directly within `include/linux/fs.h`. This file usually houses core file system data structures, and it's highly likely that the `inode` definition is located there. Let's start the search.
|
| 14/2 |
2026/01/09 20:43 |
tool |
codesearch-file-index |
0m
Model:
Args: map[SourceFile:include/linux/fs.h]
Results: map[Entities:[map[Kind:function Name:HAS_UNMAPPED_ID] map[Kind:function Name:__blockdev_direct_IO] map[Kind:function Name:__check_sticky] map[Kind:function Name:__compat_vma_mmap] map[Kind:function Name:__destroy_inode] map[Kind:function Name:__f_setown] map[Kind:function Name:__free_putname] map[Kind:function Name:__generic_file_fsync] map[Kind:function Name:__generic_file_write_iter] map[Kind:function Name:__generic_remap_file_range_prep] map[Kind:function Name:__getname_maybe_null] map[Kind:function Name:__iget] map[Kind:function Name:__inode_add_bytes] map[Kind:function Name:__inode_get_bytes] map[Kind:function Name:__inode_sub_bytes] map[Kind:function Name:__insert_inode_hash] map[Kind:function Name:__kernel_read] map[Kind:function Name:__kernel_write] map[Kind:function Name:__mark_inode_dirty] map[Kind:function Name:__register_chrdev] map[Kind:function Name:__remove_inode_hash] map[Kind:function Name:__simple_attr_check_format] map[Kind:function Name:__simple_rmdir] map[Kind:function Name:__simple_unlink] map[Kind:function Name:__unregister_chrdev] map[Kind:function Name:address_space_init_once] map[Kind:function Name:alloc_anon_inode] map[Kind:function Name:alloc_chrdev_region] map[Kind:function Name:alloc_inode] map[Kind:function Name:allow_write_access] map[Kind:function Name:always_delete_dentry] map[Kind:function Name:anon_inode_make_secure_inode] map[Kind:function Name:atime_needs_update] map[Kind:function Name:backing_file_user_path] map[Kind:function Name:blockdev_direct_IO] map[Kind:function Name:bmap] map[Kind:function Name:can_mmap_file] map[Kind:function Name:check_sticky] map[Kind:function Name:chrdev_show] map[Kind:function Name:clear_inode] map[Kind:function Name:clear_nlink] map[Kind:function Name:compat_ptr_ioctl] map[Kind:function Name:compat_vma_mmap] map[Kind:function Name:copy_splice_read] map[Kind:function Name:current_time] map[Kind:function Name:d_alloc_name] map[Kind:function Name:d_mark_dontcache] map[Kind:function Name:dcache_dir_close] map[Kind:function Name:dcache_dir_lseek] map[Kind:function Name:dcache_dir_open] map[Kind:function Name:dcache_readdir] map[Kind:function Name:deactivate_locked_super] map[Kind:function Name:deactivate_super] map[Kind:function Name:default_llseek] map[Kind:function Name:dentry_create] map[Kind:function Name:dentry_open] map[Kind:function Name:dentry_open_nonotify] map[Kind:function Name:deny_write_access] map[Kind:function Name:dir_emit] map[Kind:function Name:dir_emit_dot] map[Kind:function Name:dir_emit_dotdot] map[Kind:function Name:dir_emit_dots] map[Kind:function Name:dir_relax] map[Kind:function Name:dir_relax_shared] map[Kind:function Name:direct_write_fallback] map[Kind:function Name:discard_new_inode] map[Kind:function Name:do_pipe_flags] map[Kind:function Name:do_sys_open] map[Kind:function Name:do_truncate] map[Kind:function Name:drop_nlink] map[Kind:function Name:drop_super] map[Kind:function Name:drop_super_exclusive] map[Kind:function Name:dump_mapping] map[Kind:function Name:emergency_remount] map[Kind:function Name:emergency_sync] map[Kind:function Name:emergency_thaw_all] map[Kind:function Name:end_dirop] map[Kind:function Name:evict_inodes] map[Kind:function Name:exe_file_allow_write_access] map[Kind:function Name:exe_file_deny_write_access] map[Kind:function Name:execute_ok] map[Kind:function Name:extensible_ioctl_valid] map[Kind:function Name:f_delown] map[Kind:function Name:f_getown] map[Kind:function Name:f_setown] map[Kind:function Name:fasync_alloc] map[Kind:function Name:fasync_free] map[Kind:function Name:fasync_helper] map[Kind:function Name:fasync_insert_entry] map[Kind:function Name:fasync_remove_entry] map[Kind:function Name:fd_statfs] map[Kind:function Name:file_accessed] map[Kind:function Name:file_check_and_advance_wb_err] map[Kind:function Name:file_clone_open] map[Kind:function Name:file_dentry] map[Kind:function Name:file_end_write] map[Kind:function Name:file_f_owner] map[Kind:function Name:file_f_owner_allocate] map[Kind:function Name:file_fdatawait_range] map[Kind:function Name:file_inode] map[Kind:function Name:file_is_dax] map[Kind:function Name:file_mnt_idmap] map[Kind:function Name:file_modified] map[Kind:function Name:file_open_name] map[Kind:function Name:file_open_root] map[Kind:function Name:file_open_root_mnt] map[Kind:function Name:file_path] map[Kind:function Name:file_permission] map[Kind:function Name:file_ra_state_init] map[Kind:function Name:file_remove_privs] map[Kind:function Name:file_set_fsnotify_mode] map[Kind:function Name:file_start_write] map[Kind:function Name:file_start_write_trylock] map[Kind:function Name:file_update_time] map[Kind:function Name:file_user_inode] map[Kind:function Name:file_user_path] map[Kind:function Name:file_write_and_wait] map[Kind:function Name:file_write_and_wait_range] map[Kind:function Name:file_write_not_started] map[Kind:function Name:file_write_started] map[Kind:function Name:filemap_flush_range] map[Kind:function Name:filemap_invalidate_lock] map[Kind:function Name:filemap_invalidate_lock_shared] map[Kind:function Name:filemap_invalidate_lock_two] map[Kind:function Name:filemap_invalidate_trylock_shared] map[Kind:function Name:filemap_invalidate_unlock] map[Kind:function Name:filemap_invalidate_unlock_shared] map[Kind:function Name:filemap_invalidate_unlock_two] map[Kind:function Name:filemap_read] map[Kind:function Name:filemap_splice_read] map[Kind:function Name:files_init] map[Kind:function Name:files_maxfiles_init] map[Kind:function Name:filesystems_freeze] map[Kind:function Name:filesystems_thaw] map[Kind:function Name:fill_mg_cmtime] map[Kind:function Name:filp_close] map[Kind:function Name:filp_open] map[Kind:function Name:find_inode_by_ino_rcu] map[Kind:function Name:find_inode_nowait] map[Kind:function Name:find_inode_rcu] map[Kind:function Name:finish_no_open] map[Kind:function Name:finish_open] map[Kind:function Name:finish_open_simple] map[Kind:function Name:fixed_size_llseek] map[Kind:function Name:free_anon_bdev] map[Kind:function Name:free_inode_nonrcu] map[Kind:function Name:fsuidgid_has_mapping] map[Kind:function Name:generic_atomic_write_valid] map[Kind:function Name:generic_check_addressable] map[Kind:function Name:generic_ci_validate_strict_name] map[Kind:function Name:generic_fadvise] map[Kind:function Name:generic_file_direct_write] map[Kind:function Name:generic_file_fsync] map[Kind:function Name:generic_file_llseek] map[Kind:function Name:generic_file_llseek_size] map[Kind:function Name:generic_file_mmap] map[Kind:function Name:generic_file_mmap_prepare] map[Kind:function Name:generic_file_open] map[Kind:function Name:generic_file_read_iter] map[Kind:function Name:generic_file_readonly_mmap] map[Kind:function Name:generic_file_readonly_mmap_prepare] map[Kind:function Name:generic_file_rw_checks] map[Kind:function Name:generic_file_write_iter] map[Kind:function Name:generic_fill_statx_atomic_writes] map[Kind:function Name:generic_fill_statx_attr] map[Kind:function Name:generic_fillattr] map[Kind:function Name:generic_llseek_cookie] map[Kind:function Name:generic_perform_write] map[Kind:function Name:generic_permission] map[Kind:function Name:generic_read_dir] map[Kind:function Name:generic_remap_file_range_prep] map[Kind:function Name:generic_set_sb_d_ops] map[Kind:function Name:generic_shutdown_super] map[Kind:function Name:generic_update_time] map[Kind:function Name:generic_write_check_limits] map[Kind:function Name:generic_write_checks] map[Kind:function Name:generic_write_checks_count] map[Kind:function Name:generic_write_sync] map[Kind:function Name:get_anon_bdev] map[Kind:function Name:get_file] map[Kind:function Name:get_file_active] map[Kind:function Name:get_file_rcu] map[Kind:function Name:get_filesystem] map[Kind:function Name:get_fs_type] map[Kind:function Name:get_max_files] map[Kind:function Name:get_next_ino] map[Kind:function Name:get_write_access] map[Kind:function Name:getname] map[Kind:function Name:getname_flags] map[Kind:function Name:getname_kernel] map[Kind:function Name:getname_maybe_null] map[Kind:function Name:getname_uflags] map[Kind:function Name:i_blocksize] map[Kind:function Name:i_gid_into_vfsgid] map[Kind:function Name:i_gid_needs_update] map[Kind:function Name:i_gid_read] map[Kind:function Name:i_gid_update] map[Kind:function Name:i_gid_write] map[Kind:function Name:i_mmap_assert_locked] map[Kind:function Name:i_mmap_assert_write_locked] map[Kind:function Name:i_mmap_lock_read] map[Kind:function Name:i_mmap_lock_write] map[Kind:function Name:i_mmap_trylock_read] map[Kind:function Name:i_mmap_trylock_write] map[Kind:function Name:i_mmap_unlock_read] map[Kind:function Name:i_mmap_unlock_write] map[Kind:function Name:i_readcount_dec] map[Kind:function Name:i_readcount_inc] map[Kind:function Name:i_size_read] map[Kind:function Name:i_size_write] map[Kind:function Name:i_uid_into_vfsuid] map[Kind:function Name:i_uid_needs_update] map[Kind:function Name:i_uid_read] map[Kind:function Name:i_uid_update] map[Kind:function Name:i_uid_write] map[Kind:function Name:i_user_ns] map[Kind:function Name:icount_read] map[Kind:function Name:iget5_locked] map[Kind:function Name:iget5_locked_rcu] map[Kind:function Name:iget_failed] map[Kind:function Name:iget_locked] map[Kind:function Name:igrab] map[Kind:function Name:ihold] map[Kind:function Name:ilookup] map[Kind:function Name:ilookup5] map[Kind:function Name:ilookup5_nowait] map[Kind:function Name:imajor] map[Kind:function Name:iminor] map[Kind:function Name:in_group_or_capable] map[Kind:function Name:inc_nlink] map[Kind:function Name:init_special_inode] map[Kind:function Name:init_sync_kiocb] map[Kind:function Name:inode_add_bytes] map[Kind:function Name:inode_bit_waitqueue] map[Kind:function Name:inode_dec_link_count] map[Kind:function Name:inode_dio_begin] map[Kind:function Name:inode_dio_end] map[Kind:function Name:inode_dio_finished] map[Kind:function Name:inode_dio_wait] map[Kind:function Name:inode_dio_wait_interruptible] map[Kind:function Name:inode_fake_hash] map[Kind:function Name:inode_fsgid_set] map[Kind:function Name:inode_fsuid_set] map[Kind:function Name:inode_generic_drop] map[Kind:function Name:inode_get_atime] map[Kind:function Name:inode_get_atime_nsec] map[Kind:function Name:inode_get_atime_sec] map[Kind:function Name:inode_get_bytes] map[Kind:function Name:inode_get_ctime] map[Kind:function Name:inode_get_ctime_nsec] map[Kind:function Name:inode_get_ctime_sec] map[Kind:function Name:inode_get_mtime] map[Kind:function Name:inode_get_mtime_nsec] map[Kind:function Name:inode_get_mtime_sec] map[Kind:function Name:inode_has_no_xattr] map[Kind:function Name:inode_inc_link_count] map[Kind:function Name:inode_init] map[Kind:function Name:inode_init_always] map[Kind:function Name:inode_init_always_gfp] map[Kind:function Name:inode_init_early] map[Kind:function Name:inode_init_once] map[Kind:function Name:inode_init_owner] map[Kind:function Name:inode_insert5] map[Kind:function Name:inode_is_dirtytime_only] map[Kind:function Name:inode_is_locked] map[Kind:function Name:inode_is_open_for_write] map[Kind:function Name:inode_just_drop] map[Kind:function Name:inode_lock] map[Kind:function Name:inode_lock_killable] map[Kind:function Name:inode_lock_nested] map[Kind:function Name:inode_lock_shared] map[Kind:function Name:inode_lock_shared_killable] map[Kind:function Name:inode_lock_shared_nested] map[Kind:function Name:inode_lru_list_add] map[Kind:function Name:inode_needs_sync] map[Kind:function Name:inode_newsize_ok] map[Kind:function Name:inode_nohighmem] map[Kind:function Name:inode_owner_or_capable] map[Kind:function Name:inode_permission] map[Kind:function Name:inode_sb_list_add] map[Kind:function Name:inode_set_atime] map[Kind:function Name:inode_set_atime_to_ts] map[Kind:function Name:inode_set_bytes] map[Kind:function Name:inode_set_cached_link] map[Kind:function Name:inode_set_ctime] map[Kind:function Name:inode_set_ctime_current] map[Kind:function Name:inode_set_ctime_deleg] map[Kind:function Name:inode_set_ctime_to_ts] map[Kind:function Name:inode_set_flags] map[Kind:function Name:inode_set_mtime] map[Kind:function Name:inode_set_mtime_to_ts] map[Kind:function Name:inode_state_assign] map[Kind:function Name:inode_state_assign_raw] map[Kind:function Name:inode_state_clear] map[Kind:function Name:inode_state_clear_raw] map[Kind:function Name:inode_state_read] map[Kind:function Name:inode_state_read_once] map[Kind:function Name:inode_state_replace] map[Kind:function Name:inode_state_replace_raw] map[Kind:function Name:inode_state_set] map[Kind:function Name:inode_state_set_raw] map[Kind:function Name:inode_sub_bytes] map[Kind:function Name:inode_trylock] map[Kind:function Name:inode_trylock_shared] map[Kind:function Name:inode_unhashed] map[Kind:function Name:inode_unlock] map[Kind:function Name:inode_unlock_shared] map[Kind:function Name:inode_update_time] map[Kind:function Name:inode_update_timestamps] map[Kind:function Name:inode_wake_up_bit] map[Kind:function Name:inode_wrong_type] map[Kind:function Name:insert_inode_hash] map[Kind:function Name:insert_inode_locked] map[Kind:function Name:insert_inode_locked4] map[Kind:function Name:iocb_flags] map[Kind:function Name:iocb_is_dsync] map[Kind:function Name:iput] map[Kind:function Name:iput_not_last] map[Kind:function Name:is_bad_inode] map[Kind:function Name:is_dot_dotdot] map[Kind:function Name:is_empty_dir_inode] map[Kind:function Name:is_idmapped_mnt] map[Kind:function Name:is_mgtime] map[Kind:function Name:is_root_inode] map[Kind:function Name:is_subdir] map[Kind:function Name:is_sxid] map[Kind:function Name:is_sync_kiocb] map[Kind:function Name:is_uncached_acl] map[Kind:function Name:is_zero_ino] map[Kind:function Name:iter_file_splice_write] map[Kind:function Name:iterate_dir] map[Kind:function Name:iterate_supers] map[Kind:function Name:iterate_supers_type] map[Kind:function Name:iunique] map[Kind:function Name:kernel_file_open] map[Kind:function Name:kernel_read] map[Kind:function Name:kernel_tmpfile_open] map[Kind:function Name:kernel_write] map[Kind:function Name:kfree_link] map[Kind:function Name:kill_anon_super] map[Kind:function Name:kill_block_super] map[Kind:function Name:kill_fasync] map[Kind:function Name:kiocb_clone] map[Kind:function Name:kiocb_end_write] map[Kind:function Name:kiocb_modified] map[Kind:function Name:kiocb_set_rw_flags] map[Kind:function Name:kiocb_start_write] map[Kind:function Name:list_bdev_fs_names] map[Kind:function Name:lock_two_nondirectories] map[Kind:function Name:lockdep_annotate_inode_mutex_key] map[Kind:function Name:locked_recursive_removal] map[Kind:function Name:make_bad_inode] map[Kind:function Name:make_empty_dir_inode] map[Kind:function Name:mapping_allow_writable] map[Kind:function Name:mapping_deny_writable] map[Kind:function Name:mapping_map_writable] map[Kind:function Name:mapping_mapped] map[Kind:function Name:mapping_tagged] map[Kind:function Name:mapping_unmap_writable] map[Kind:function Name:mapping_writably_mapped] map[Kind:function Name:mark_inode_dirty] map[Kind:function Name:mark_inode_dirty_sync] map[Kind:function Name:may_open_dev] map[Kind:function Name:may_setattr] map[Kind:function Name:mode_strip_sgid] map[Kind:function Name:mount_subtree] map[Kind:function Name:name_contains_dotdot] map[Kind:function Name:new_inode] map[Kind:function Name:new_inode_pseudo] map[Kind:function Name:no_seek_end_llseek] map[Kind:function Name:no_seek_end_llseek_size] map[Kind:function Name:nonseekable_open] map[Kind:function Name:noop_direct_IO] map[Kind:function Name:noop_fsync] map[Kind:function Name:noop_llseek] map[Kind:function Name:notify_change] map[Kind:function Name:open_exec] map[Kind:function Name:page_get_link] map[Kind:function Name:page_get_link_raw] map[Kind:function Name:page_put_link] map[Kind:function Name:page_readlink] map[Kind:function Name:page_symlink] map[Kind:function Name:path_is_under] map[Kind:function Name:path_noexec] map[Kind:function Name:path_permission] map[Kind:function Name:put_filesystem] map[Kind:function Name:put_write_access] map[Kind:function Name:putname] map[Kind:function Name:ra_has_index] map[Kind:function Name:readlink_copy] map[Kind:function Name:refname] map[Kind:function Name:register_chrdev] map[Kind:function Name:register_chrdev_region] map[Kind:function Name:register_filesystem] map[Kind:function Name:remap_verify_area] map[Kind:function Name:remove_inode_hash] map[Kind:function Name:retire_super] map[Kind:function Name:rw_verify_area] map[Kind:function Name:send_sigio] map[Kind:function Name:send_sigurg] map[Kind:function Name:set_anon_super] map[Kind:function Name:set_anon_super_fc] map[Kind:function Name:set_nlink] map[Kind:function Name:setattr_copy] map[Kind:function Name:setattr_prepare] map[Kind:function Name:setattr_should_drop_sgid] map[Kind:function Name:setattr_should_drop_suidgid] map[Kind:function Name:sget] map[Kind:function Name:sget_dev] map[Kind:function Name:sget_fc] map[Kind:function Name:simple_attr_open] map[Kind:function Name:simple_attr_read] map[Kind:function Name:simple_attr_release] map[Kind:function Name:simple_attr_write] map[Kind:function Name:simple_attr_write_signed] map[Kind:function Name:simple_done_creating] map[Kind:function Name:simple_empty] map[Kind:function Name:simple_fill_super] map[Kind:function Name:simple_get_link] map[Kind:function Name:simple_getattr] map[Kind:function Name:simple_inode_init_ts] map[Kind:function Name:simple_link] map[Kind:function Name:simple_lookup] map[Kind:function Name:simple_nosetlease] map[Kind:function Name:simple_offset_add] map[Kind:function Name:simple_offset_destroy] map[Kind:function Name:simple_offset_init] map[Kind:function Name:simple_offset_remove] map[Kind:function Name:simple_offset_rename] map[Kind:function Name:simple_offset_rename_exchange] map[Kind:function Name:simple_open] map[Kind:function Name:simple_pin_fs] map[Kind:function Name:simple_read_from_buffer] map[Kind:function Name:simple_recursive_removal] map[Kind:function Name:simple_release_fs] map[Kind:function Name:simple_remove_by_name] map[Kind:function Name:simple_rename] map[Kind:function Name:simple_rename_exchange] map[Kind:function Name:simple_rename_timestamp] map[Kind:function Name:simple_rmdir] map[Kind:function Name:simple_setattr] map[Kind:function Name:simple_start_creating] map[Kind:function Name:simple_statfs] map[Kind:function Name:simple_transaction_get] map[Kind:function Name:simple_transaction_read] map[Kind:function Name:simple_transaction_release] map[Kind:function Name:simple_transaction_set] map[Kind:function Name:simple_unlink] map[Kind:function Name:simple_write_begin] map[Kind:function Name:simple_write_to_buffer] map[Kind:function Name:stream_open] map[Kind:function Name:super_set_sysfs_name_bdev] map[Kind:function Name:super_set_sysfs_name_generic] map[Kind:function Name:super_set_sysfs_name_id] map[Kind:function Name:super_set_sysfs_name_uuid] map[Kind:function Name:super_set_uuid] map[Kind:function Name:super_setup_bdi] map[Kind:function Name:super_setup_bdi_name] map[Kind:function Name:sync_file_range] map[Kind:function Name:sync_filesystem] map[Kind:function Name:sync_inode_metadata] map[Kind:function Name:timestamp_truncate] map[Kind:function Name:touch_atime] map[Kind:function Name:uncached_acl_sentinel] map[Kind:function Name:unlock_new_inode] map[Kind:function Name:unlock_two_nondirectories] map[Kind:function Name:unregister_chrdev] map[Kind:function Name:unregister_chrdev_region] map[Kind:function Name:unregister_filesystem] map[Kind:function Name:user_statfs] map[Kind:function Name:vfs_caches_init] map[Kind:function Name:vfs_caches_init_early] map[Kind:function Name:vfs_clone_file_range] map[Kind:function Name:vfs_copy_file_range] map[Kind:function Name:vfs_create] map[Kind:function Name:vfs_dedupe_file_range] map[Kind:function Name:vfs_dedupe_file_range_one] map[Kind:function Name:vfs_empty_path] map[Kind:function Name:vfs_fadvise] map[Kind:function Name:vfs_fallocate] map[Kind:function Name:vfs_fchmod] map[Kind:function Name:vfs_fchown] map[Kind:function Name:vfs_fstat] map[Kind:function Name:vfs_fstatat] map[Kind:function Name:vfs_fsync] map[Kind:function Name:vfs_fsync_range] map[Kind:function Name:vfs_get_link] map[Kind:function Name:vfs_getattr] map[Kind:function Name:vfs_getattr_nosec] map[Kind:function Name:vfs_iocb_iter_read] map[Kind:function Name:vfs_iocb_iter_write] map[Kind:function Name:vfs_iter_read] map[Kind:function Name:vfs_iter_write] map[Kind:function Name:vfs_link] map[Kind:function Name:vfs_llseek] map[Kind:function Name:vfs_lstat] map[Kind:function Name:vfs_mkdir] map[Kind:function Name:vfs_mknod] map[Kind:function Name:vfs_mkobj] map[Kind:function Name:vfs_mmap] map[Kind:function Name:vfs_mmap_prepare] map[Kind:function Name:vfs_read] map[Kind:function Name:vfs_readlink] map[Kind:function Name:vfs_rename] map[Kind:function Name:vfs_rmdir] map[Kind:function Name:vfs_setpos] map[Kind:function Name:vfs_stat] map[Kind:function Name:vfs_statfs] map[Kind:function Name:vfs_symlink] map[Kind:function Name:vfs_truncate] map[Kind:function Name:vfs_unlink] map[Kind:function Name:vfs_utimes] map[Kind:function Name:vfs_whiteout] map[Kind:function Name:vfs_write] map[Kind:function Name:vfsmount_to_propagation_flags] map[Kind:function Name:vma_is_dax] map[Kind:function Name:vma_is_fsdax] map[Kind:function Name:wait_on_new_inode] map[Kind:function Name:wrap_directory_iterator]] Missing:false]
|
| 15/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: **Debugging a Suspected Race Condition**
Okay, so I've got a lot of entities to sift through. My initial hunch, given the "write of 4 bytes" in the report, is that the race condition is happening on the `i_atime_nsec` field. That would make sense, assuming `i_atime_nsec` is a 32-bit (4-byte) value. Let me just quickly confirm the implementation of `inode_set_atime_to_ts`.
*Yep, it looks like it's just setting the `tv_sec` and `tv_nsec` values.*
Now, I need to verify the size of `i_atime_nsec` within the `struct inode`. I'll need to locate the definition of `struct inode`. Typically, that definition resides in `include/linux/fs.h`. It appears that my usual tools aren't cooperating here. I'm going to try to zero in on it. I can't just grep the file contents, unfortunately. I could try to search the file, but I also see that `inode_set_atime_to_ts` takes `struct inode` as an argument. Let me try using that as a starting point. Let's see if I can find `inode_init_always` which also takes a `struct inode` as an argument to help me locate the definition.
|
| 16/2 |
2026/01/09 20:43 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:inode_init_always SourceFile:fs/inode.c]
Results: map[Missing:false SourceCode:2880: static inline int inode_init_always(struct super_block *sb, struct inode *inode)
2881: {
2882: return inode_init_always_gfp(sb, inode, GFP_NOFS);
2883: }
SourceFile:include/linux/fs.h]
|
| 17/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: **Dissecting a Potential Data Race in the USB Driver**
Okay, so I'm looking at this KCSAN report indicating a data race in the USB driver, specifically involving the `atime` (access time) update of a USB device file node (`/dev/bus/usb/...`). I know this means two or more threads are writing to the same memory location concurrently. The report points to a 4-byte write at a specific address, which strongly suggests we're dealing with `i_atime_nsec`, the nanosecond component of the access time within the `inode` structure. Given this is a 64-bit kernel, I believe `i_atime_nsec` will be `u32`. This has me thinking about the `struct inode` layout, and how the `atime` fields (`i_atime_sec` and `i_atime_nsec`) are handled.
The race appears to be happening in `usbdev_do_ioctl`, specifically after the `ioctl` operation itself has completed successfully. This function explicitly calls `inode_set_atime_to_ts`, which updates the `atime`. Normally, `ioctl` calls don't automatically update `atime`, so the design choice here is notable.
My investigation leads me to believe the driver's use of `usb_lock_device(dev)` is the crux of the issue. The critical section *protects* the `ioctl` processing, preventing concurrent calls. However, the `inode_set_atime_to_ts` call, which does the actual timestamp update, happens *outside* this critical section. This means that after `usb_unlock_device`, the timestamp updates could be happening concurrently.
Now, the important question: Is this harmful?
* It is not related to a critical kernel internal state.
* This race is writing to the file system metadata.
* Given that the updates are closely timed (using `current_time`), the resulting `atime` value will be almost correct. The worst-case scenario is a slightly mixed up timestamp (one thread wins, or the nanosecond value from one is combined with the second value from another).
* However, the write itself is atomic (it's a 32-bit integer write on x86_64, which is atomic). There is no risk of memory corruption or anything like that.
Typically, file systems protect `atime` updates via locks (e.g. `inode_lock`) when they occur during `read` or `write`. Here, because the update happens after the `ioctl` (which is a driver level call) in the driver, it's not under VFS protection.
The race is likely "benign". It's a timestamp; and given the nature of the race, it's difficult to see a way that a slightly inaccurate `atime` would break anything.
I should confirm this by checking if the inode is involved in any invariants which could be impacted.
I will double check on the exact type of `i_atime_nsec` type, just to be sure.
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| 18/2 |
2026/01/09 20:43 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:inode_get_atime_sec SourceFile:include/linux/fs.h]
Results: map[Missing:false SourceCode:1601: static inline time64_t inode_get_atime_sec(const struct inode *inode)
1602: {
1603: return inode->i_atime_sec;
1604: }
SourceFile:include/linux/fs.h]
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| 19/2 |
2026/01/09 20:43 |
llm |
expert |
0m
Model:
Thoughts: Okay, here's my interpretation of what's going on, formatted as you requested:
**Deconstructing Time Representation in the System**
Alright, so I'm seeing a return of `time64_t` here. Right, that's what I'd expect for handling timestamps in the modern context, especially given the potential for dealing with very large values and avoiding the Y2038 problem. I'm assuming this implies a 64-bit integer type, likely representing seconds (or perhaps some other unit) since the epoch, which gives us plenty of room for dates far into the future. It's the standard.
And then I'm also noticing a call to `inode_get_atime_nsec`. Ah, that's important. So it looks like we're diving into retrieving the *nanosecond* resolution of an inode's access time. The "atime" is the last access time of a file or directory. That's a key piece of metadata. Now, I have to consider whether this needs some extra work. The `inode_` prefix tells me this function likely operates at a fairly low level, maybe even kernel-level. I'll need to check how it actually stores and provides these nanosecond values. Are we dealing with some internal structure, and if so, how is it accessed? Is it a single field in a structure or is there an internal method? Is there any potential for data loss or inconsistencies? Does this mean we're working on something that requires high-precision time tracking? I'll have to investigate that further.
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| 20/2 |
2026/01/09 20:44 |
tool |
codesearch-definition-source |
0m
Model:
Args: map[IncludeLines:true Name:inode_get_atime_nsec SourceFile:include/linux/fs.h]
Results: map[Missing:false SourceCode:1606: static inline long inode_get_atime_nsec(const struct inode *inode)
1607: {
1608: return inode->i_atime_nsec;
1609: }
SourceFile:include/linux/fs.h]
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| 21/2 |
2026/01/09 20:44 |
llm |
expert |
1m
Model:
Thoughts: **KCSAN Report Analysis: Benign Race on i_atime_nsec in usbdev_do_ioctl**
Okay, so KCSAN is flagging a data race in the USB driver, specifically in `drivers/usb/core/devio.c`. It looks like `usbdev_do_ioctl` is updating `i_atime_nsec` without holding the appropriate lock, `usb_lock_device`, which is weird because most *other* time updates in that function *are* protected. The stack trace points to line 1623 in `include/linux/fs.h`, specifically `inode->i_atime_nsec = ts.tv_nsec;` inside of `inode_set_atime_to_ts`.
Here's my thought process:
* **Data Type and Size:** First, I needed to figure out the size of `i_atime_nsec`. On a 64-bit x86 system (implied by the `do_syscall_64` stack trace), `long` is 8 bytes. The report indicates a "write of 4 bytes," so it's a 4-byte write. This means that `i_atime_nsec` is likely an `u32` or similar. The `ts.tv_nsec` in `timespec64` is an 8-byte `long`. So, the assignment is effectively truncating/casting the `long` to fit into the `u32`. This truncation is probably okay, itβs designed to be a fraction of a second.
* **Race Condition:** Because itβs a 4-byte write to an aligned `u32`, this is an atomic operation. This means a race *could* happen, and the last writer "wins," but this results in only a small amount of jitter in the timestamp. No memory corruption, just slightly inaccurate atime.
* **Context:** `usbdev_do_ioctl` is called through `usbdev_ioctl` which is, in turn, called by user-space. Successful ioctls result in atime updates; failed calls do not.
* **Benign Nature of Atime Race:** It's common for reading `atime` and `mtime` to *not* be protected for performance reasons. Atime itself is usually not super critical, and the race we have here is about "access time". It is intended to indicate the last *access* of a file, via reading or writing. The `atime` is *not* used for kernel integrity or control flow (normally), so losing a few nanoseconds isn't consequential. The standard VFS calls to update time use `file_update_time` which *does* take into account mount flags like `noatime`, but this ioctl path bypasses it. I think the usb driver does this directly for efficiency.
* **Inode Validity:** We are certain that the inode is valid because `usbdev_ioctl` is called *with* a file handle, which has a reference to the inode. So, no race on inode deallocation.
* **Why a Race?:** The driver author likely didn't feel atime needed protection for every ioctl, or maybe thought that the locking around the ioctl itself was sufficient (but it's not). The fact that the mtime updates are protected by the lock indicates the possibility that the atime race is an oversight (or a deliberate efficiency choice).
* **Side Effects:** The stack trace only shows this *one* race. If there were other races, KCSAN would likely report them separately. The `usb_lock_device` protects other fields.
* **Bitfields?** I considered if `i_atime_nsec` could be a bitfield, but that is unlikely. We usually see "read-modify-write" races or a bitfield races.
* **Confirmatory Steps:** I confirmed that the stack trace does point to the intended line. Also verified that all paths in `usbdev_do_ioctl` actually make the atime call, regardless of the ioctl command.
* **No Other Fields:** I also checked if any other fields were involved in the `usbdev_ioctl` routine (that aren't already protected), and it looks like itβs only this specific `inode` access.
* **Edge Cases and Final Thoughts:** The atime is generally for access tracking and not critical. I've considered and eliminated any cases where this could lead to security issues.
Therefore, given these points, the race on `i_atime_nsec` in `usbdev_do_ioctl` is **benign**. It's a timestamp jitter, but not a data corruption or security problem. Also, this function
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| 22/2 |
2026/01/09 20:45 |
tool |
set-results |
0m
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Args:
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| 23/2 |
2026/01/09 20:45 |
llm |
expert |
0m
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