WARNING: suspicious RCU usage in mas_start (2)

Status: upstream: reported C repro on 2026/09/14 21:26
Subsystems: block
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+b48868c46e62c1c4cb2c@syzkaller.appspotmail.com
First crash: 15h52m, last: 8h52m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
bb2a7ea8 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING: suspicious RCU usage in mas_start (2) 2026/09/15 02:47 2026/09/15 02:47 2026/09/15 03:23 81a27d1a
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Title Replies (including bot) Last reply
[syzbot] [block?] WARNING: suspicious RCU usage in mas_start (2) 0 (1) 2026/09/14 21:26
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING: suspicious RCU usage in mas_start kernfs 4 syz, C error done 23 1266d 1299d 22/29 fixed on 2023/06/08 14:41

Sample crash report:
=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
lib/maple_tree.c:720 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
locks held by syz-executor208/5631: 1, last CPU#1:
 #0: ffff8880792b60a0 (&ctx->uring_lock){+.+.}-{4:4}, at: tctx_task_work_run+0x2d3/0xa80 io_uring/tw.c:92

stack backtrace:
CPU: 1 UID: 0 PID: 5631 Comm: syz-executor208 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 lockdep_rcu_suspicious+0x140/0x1d0 kernel/locking/lockdep.c:6972
 mas_root lib/maple_tree.c:720 [inline]
 mas_start+0x3cc/0x640 lib/maple_tree.c:1250
 mas_state_walk lib/maple_tree.c:3006 [inline]
 mas_walk+0x1db/0x490 lib/maple_tree.c:4458
 ublk_try_buf_match drivers/block/ublk_drv.c:5639 [inline]
 ublk_init_iod+0x5d2/0x1120 drivers/block/ublk_drv.c:521
 ublk_dispatch_req+0x97/0x9c0 drivers/block/ublk_drv.c:1776
 tctx_task_work_run+0x73d/0xa80 io_uring/tw.c:96
 tctx_task_work+0x3f/0x60 io_uring/tw.c:133
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x73a/0x2360 kernel/exit.c:1011
 do_group_exit+0x22d/0x2f0 kernel/exit.c:1154
 __do_sys_exit_group kernel/exit.c:1165 [inline]
 __se_sys_exit_group kernel/exit.c:1163 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1163
 x64_sys_call+0x18c6/0x18d0 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6413fb1325
Code: Unable to access opcode bytes at 0x7f6413fb12fb.
RSP: 002b:00007ffec9819178 EFLAGS: 00000206 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f6413fb1325
RDX: 00000000000000e7 RSI: ffffffffffffffd8 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f641404a158 R14: 00007f641404c408 R15: 00007f641404c420
 </TASK>
I/O error, dev ublkb0, sector 0 op 0x0:(READ) flags 0x800000 phys_seg 1 prio class 2
Buffer I/O error on dev ublkb0, logical block 0, async page read

Crashes (15):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/14 23:04 upstream 704340f1cd0d 924033e8 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING: suspicious RCU usage in mas_start
2026/09/14 21:31 upstream 704340f1cd0d 924033e8 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING: suspicious RCU usage in mas_start
2026/09/14 20:16 upstream 704340f1cd0d 924033e8 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream WARNING: suspicious RCU usage in mas_start
2026/09/14 20:37 upstream 50d05c7c76c9 924033e8 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 WARNING: suspicious RCU usage in mas_start
2026/09/14 20:34 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 5445d6419962 924033e8 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: suspicious RCU usage in mas_start
2026/09/15 02:41 upstream 587858367581 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root WARNING: suspicious RCU usage in mas_start
2026/09/15 02:39 upstream 587858367581 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root WARNING: suspicious RCU usage in mas_start
2026/09/15 02:38 upstream 587858367581 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root WARNING: suspicious RCU usage in mas_start
2026/09/14 19:49 upstream 704340f1cd0d 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING: suspicious RCU usage in mas_start
2026/09/14 19:46 upstream 704340f1cd0d 924033e8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream WARNING: suspicious RCU usage in mas_start
2026/09/14 19:45 upstream 704340f1cd0d 924033e8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream WARNING: suspicious RCU usage in mas_start
2026/09/14 20:06 upstream 50d05c7c76c9 924033e8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 WARNING: suspicious RCU usage in mas_start
2026/09/14 20:00 upstream 50d05c7c76c9 924033e8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 WARNING: suspicious RCU usage in mas_start
2026/09/14 19:43 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 5445d6419962 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: suspicious RCU usage in mas_start
2026/09/14 19:41 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 5445d6419962 924033e8 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING: suspicious RCU usage in mas_start
* Struck through repros no longer work on HEAD.