possible deadlock in kernfs_fop_write_iter

Status: auto-obsoleted due to no activity on 2025/05/17 20:05
Reported-by: syzbot+9263281e474e3ecfc8ca@syzkaller.appspotmail.com
First crash: 631d, last: 534d
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in kernfs_fop_write_iter kernfs 4 14 729d 754d 0/29 auto-obsoleted due to no activity on 2024/10/05 00:05
linux-6.6 possible deadlock in kernfs_fop_write_iter 4 1 332d 332d 0/2 auto-obsoleted due to no activity on 2025/12/05 21:08
upstream possible deadlock in kernfs_fop_write_iter (2) kernfs 4 139 140d 650d 0/29 auto-obsoleted due to no activity on 2026/05/17 16:33
upstream possible deadlock in kernfs_fop_write_iter (3) kernfs prio:low 4 4 11d 19d 0/29 upstream: reported on 2026/07/07 14:24
linux-5.15 possible deadlock in kernfs_fop_write_iter (2) 4 1 420d 420d 0/3 auto-obsoleted due to no activity on 2025/09/09 09:34

Sample crash report:
loop7: detected capacity change from 0 to 512
EXT4-fs (loop7): mounted filesystem without journal. Opts: bsddf,,errors=continue. Quota mode: none.
======================================================
WARNING: possible circular locking dependency detected
5.15.178-syzkaller #0 Not tainted
------------------------------------------------------
syz.7.2124/14598 is trying to acquire lock:
ffff888061ae3488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e7/0x4f0 fs/kernfs/file.c:287

but task is already holding lock:
ffff8880619d3c68 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x2ab/0xfa0 fs/splice.c:635

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (&pipe->mutex/1){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       iter_file_splice_write+0x2ab/0xfa0 fs/splice.c:635
       do_splice_from fs/splice.c:767 [inline]
       do_splice+0xfe6/0x1790 fs/splice.c:1079
       __do_splice fs/splice.c:1144 [inline]
       __do_sys_splice fs/splice.c:1350 [inline]
       __se_sys_splice+0x340/0x420 fs/splice.c:1332
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #6 (sb_writers#3){.+.+}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1813 [inline]
       sb_start_write include/linux/fs.h:1883 [inline]
       file_start_write include/linux/fs.h:3044 [inline]
       lo_write_bvec+0x1a3/0x740 drivers/block/loop.c:315
       lo_write_simple drivers/block/loop.c:338 [inline]
       do_req_filebacked drivers/block/loop.c:656 [inline]
       loop_handle_cmd drivers/block/loop.c:2234 [inline]
       loop_process_work+0x2309/0x2af0 drivers/block/loop.c:2274
       process_one_work+0x8a1/0x10c0 kernel/workqueue.c:2310
       worker_thread+0xaca/0x1280 kernel/workqueue.c:2457
       kthread+0x3f6/0x4f0 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #5 ((work_completion)(&worker->work)){+.+.}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       process_one_work+0x7f1/0x10c0 kernel/workqueue.c:2286
       worker_thread+0xaca/0x1280 kernel/workqueue.c:2457
       kthread+0x3f6/0x4f0 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #4 ((wq_completion)loop8){+.+.}-{0:0}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       flush_workqueue+0x170/0x1610 kernel/workqueue.c:2830
       drain_workqueue+0xc5/0x390 kernel/workqueue.c:2995
       destroy_workqueue+0x7b/0xae0 kernel/workqueue.c:4439
       __loop_clr_fd+0x241/0xbe0 drivers/block/loop.c:1383
       blkdev_put_whole block/bdev.c:692 [inline]
       blkdev_put+0x455/0x790 block/bdev.c:954
       deactivate_locked_super+0xa0/0x110 fs/super.c:335
       cleanup_mnt+0x44e/0x500 fs/namespace.c:1143
       task_work_run+0x129/0x1a0 kernel/task_work.c:188
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop+0x106/0x130 kernel/entry/common.c:181
       exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:214
       __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
       syscall_exit_to_user_mode+0x5d/0x240 kernel/entry/common.c:307
       do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #3 (&lo->lo_mutex){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_killable_nested+0x17/0x20 kernel/locking/mutex.c:758
       lo_open+0x68/0x100 drivers/block/loop.c:2055
       blkdev_get_whole+0x94/0x390 block/bdev.c:669
       blkdev_get_by_dev+0x2bc/0xa50 block/bdev.c:824
       blkdev_open+0x138/0x2d0 block/fops.c:463
       do_dentry_open+0x807/0xfb0 fs/open.c:826
       do_open fs/namei.c:3608 [inline]
       path_openat+0x2705/0x2f20 fs/namei.c:3742
       do_filp_open+0x21c/0x460 fs/namei.c:3769
       do_sys_openat2+0x13b/0x4f0 fs/open.c:1253
       do_sys_open fs/open.c:1269 [inline]
       __do_sys_openat fs/open.c:1285 [inline]
       __se_sys_openat fs/open.c:1280 [inline]
       __x64_sys_openat+0x243/0x290 fs/open.c:1280
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #2 (&disk->open_mutex){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       blkdev_get_by_dev+0x14d/0xa50 block/bdev.c:817
       swsusp_check+0xb1/0x2c0 kernel/power/swap.c:1526
       software_resume+0xc6/0x3c0 kernel/power/hibernate.c:977
       resume_store+0xe3/0x130 kernel/power/hibernate.c:1179
       kernfs_fop_write_iter+0x3a2/0x4f0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2174 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0xacd/0xe50 fs/read_write.c:594
       ksys_write+0x1a2/0x2c0 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (system_transition_mutex/1){+.+.}-{3:3}:
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       software_resume+0x7c/0x3c0 kernel/power/hibernate.c:932
       resume_store+0xe3/0x130 kernel/power/hibernate.c:1179
       kernfs_fop_write_iter+0x3a2/0x4f0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2174 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0xacd/0xe50 fs/read_write.c:594
       ksys_write+0x1a2/0x2c0 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&of->mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain+0x1649/0x5930 kernel/locking/lockdep.c:3788
       __lock_acquire+0x1295/0x1ff0 kernel/locking/lockdep.c:5012
       lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       kernfs_fop_write_iter+0x1e7/0x4f0 fs/kernfs/file.c:287
       do_iter_readv_writev+0x594/0x7a0
       do_iter_write+0x1e6/0x760 fs/read_write.c:855
       iter_file_splice_write+0x806/0xfa0 fs/splice.c:689
       do_splice_from fs/splice.c:767 [inline]
       do_splice+0xfe6/0x1790 fs/splice.c:1079
       __do_splice fs/splice.c:1144 [inline]
       __do_sys_splice fs/splice.c:1350 [inline]
       __se_sys_splice+0x340/0x420 fs/splice.c:1332
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
  &of->mutex --> sb_writers#3 --> &pipe->mutex/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex/1);
                               lock(sb_writers#3);
                               lock(&pipe->mutex/1);
  lock(&of->mutex);

 *** DEADLOCK ***

2 locks held by syz.7.2124/14598:
 #0: ffff88807efbe460 (sb_writers#8){.+.+}-{0:0}, at: __do_splice fs/splice.c:1144 [inline]
 #0: ffff88807efbe460 (sb_writers#8){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1350 [inline]
 #0: ffff88807efbe460 (sb_writers#8){.+.+}-{0:0}, at: __se_sys_splice+0x340/0x420 fs/splice.c:1332
 #1: ffff8880619d3c68 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x2ab/0xfa0 fs/splice.c:635

stack backtrace:
CPU: 1 PID: 14598 Comm: syz.7.2124 Not tainted 5.15.178-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106
 check_noncircular+0x2f8/0x3b0 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain+0x1649/0x5930 kernel/locking/lockdep.c:3788
 __lock_acquire+0x1295/0x1ff0 kernel/locking/lockdep.c:5012
 lock_acquire+0x1db/0x4f0 kernel/locking/lockdep.c:5623
 __mutex_lock_common+0x1da/0x25a0 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 kernfs_fop_write_iter+0x1e7/0x4f0 fs/kernfs/file.c:287
 do_iter_readv_writev+0x594/0x7a0
 do_iter_write+0x1e6/0x760 fs/read_write.c:855
 iter_file_splice_write+0x806/0xfa0 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 do_splice+0xfe6/0x1790 fs/splice.c:1079
 __do_splice fs/splice.c:1144 [inline]
 __do_sys_splice fs/splice.c:1350 [inline]
 __se_sys_splice+0x340/0x420 fs/splice.c:1332
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0b2e5dcde9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0b2c446038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f0b2e7f5fa0 RCX: 00007f0b2e5dcde9
RDX: 0000000000000007 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f0b2e65e2a0 R08: 000000000000bfd1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f0b2e7f5fa0 R15: 00007fff8efe4d28
 </TASK>
kernel profiling enabled (shift: 8)

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/06 20:04 linux-5.15.y c16c81c81336 8002dd28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in kernfs_fop_write_iter
2024/11/02 01:46 linux-5.15.y 72244eab0dad f00eed24 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in kernfs_fop_write_iter
2024/11/02 01:45 linux-5.15.y 72244eab0dad f00eed24 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in kernfs_fop_write_iter
* Struck through repros no longer work on HEAD.