syzbot


possible deadlock in __unix_gc

Status: upstream: reported C repro on 2024/04/23 16:09
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+fa379358c28cc87cc307@syzkaller.appspotmail.com
Fix commit: 1971d13ffa84 af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc().
Patched on: [ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-net-next-test-gce ci2-upstream-usb], missing on: [ci-qemu2-riscv64]
First crash: 24d, last: 22d
Cause bisection: introduced by (bisect log) :
commit 47d8ac011fe1c9251070e1bd64cb10b48193ec51
Author: Michal Luczaj <mhal@rbox.co>
Date: Tue Apr 9 20:09:39 2024 +0000

  af_unix: Fix garbage collector racing against connect()

Crash: possible deadlock in __unix_gc (log)
Repro: C syz .config
  
Discussions (4)
Title Replies (including bot) Last reply
[PATCH v3 net] af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc(). 2 (2) 2024/04/25 15:50
[PATCH v2 net] af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc(). 3 (3) 2024/04/24 16:59
[PATCH v1 net-next] af_unix: Suppress false-positive lockdep splat for spin_lock() in __unix_gc(). 2 (2) 2024/04/24 02:21
[syzbot] [net?] possible deadlock in __unix_gc 2 (6) 2024/04/24 02:01
Last patch testing requests (2)
Created Duration User Patch Repo Result
2024/04/24 00:43 23m kuniyu@amazon.com patch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 4d2008430ce87061c9cefd4f83daf2d5bb323a96 OK log
2024/04/23 22:35 24m hdanton@sina.com patch https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 4d2008430ce8 OK log

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0 Not tainted
------------------------------------------------------
kworker/u8:1/11 is trying to acquire lock:
ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88807cea4e70 (&u->lock){+.+.}-{2:2}, at: __unix_gc+0x40e/0xf70 net/unix/garbage.c:302

but task is already holding lock:
ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (unix_gc_lock){+.+.}-{2:2}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
       spin_lock include/linux/spinlock.h:351 [inline]
       unix_notinflight+0x13d/0x390 net/unix/garbage.c:140
       unix_detach_fds net/unix/af_unix.c:1819 [inline]
       unix_destruct_scm+0x221/0x350 net/unix/af_unix.c:1876
       skb_release_head_state+0x100/0x250 net/core/skbuff.c:1188
       skb_release_all net/core/skbuff.c:1200 [inline]
       __kfree_skb net/core/skbuff.c:1216 [inline]
       kfree_skb_reason+0x16d/0x3b0 net/core/skbuff.c:1252
       kfree_skb include/linux/skbuff.h:1262 [inline]
       manage_oob net/unix/af_unix.c:2672 [inline]
       unix_stream_read_generic+0x1125/0x2700 net/unix/af_unix.c:2749
       unix_stream_splice_read+0x239/0x320 net/unix/af_unix.c:2981
       do_splice_read fs/splice.c:985 [inline]
       splice_file_to_pipe+0x299/0x500 fs/splice.c:1295
       do_splice+0xf2d/0x1880 fs/splice.c:1379
       __do_splice fs/splice.c:1436 [inline]
       __do_sys_splice fs/splice.c:1652 [inline]
       __se_sys_splice+0x331/0x4a0 fs/splice.c:1634
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&u->lock){+.+.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
       __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
       _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
       spin_lock include/linux/spinlock.h:351 [inline]
       __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
       process_one_work kernel/workqueue.c:3254 [inline]
       process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
       worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
       kthread+0x2f0/0x390 kernel/kthread.c:388
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(unix_gc_lock);
                               lock(&u->lock);
                               lock(unix_gc_lock);
  lock(&u->lock);

 *** DEADLOCK ***

3 locks held by kworker/u8:1/11:
 #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline]
 #0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x17c0 kernel/workqueue.c:3335
 #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline]
 #1: ffffc90000107d00 (unix_gc_work){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x17c0 kernel/workqueue.c:3335
 #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #2: ffffffff8f6ab638 (unix_gc_lock){+.+.}-{2:2}, at: __unix_gc+0x117/0xf70 net/unix/garbage.c:261

stack backtrace:
CPU: 0 PID: 11 Comm: kworker/u8:1 Not tainted 6.9.0-rc5-syzkaller-00007-g4d2008430ce8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound __unix_gc
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 __unix_gc+0x40e/0xf70 net/unix/garbage.c:302
 process_one_work kernel/workqueue.c:3254 [inline]
 process_scheduled_works+0xa10/0x17c0 kernel/workqueue.c:3335
 worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
 kthread+0x2f0/0x390 kernel/kthread.c:388
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/04/23 10:12 upstream 4d2008430ce8 21339d7b .config strace log report syz C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce possible deadlock in __unix_gc
2024/04/25 20:49 upstream e33c4963bf53 8bdc0f22 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in __unix_gc
2024/04/25 15:05 upstream e88c4cfcb7b8 8bdc0f22 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root possible deadlock in __unix_gc
2024/04/23 17:18 upstream 71b1543c83d6 21339d7b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in __unix_gc
2024/04/23 17:18 upstream 71b1543c83d6 21339d7b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root possible deadlock in __unix_gc
* Struck through repros no longer work on HEAD.