possible deadlock in kernfs_fop_write_iter (2)

Status: auto-obsoleted due to no activity on 2025/09/09 09:34
Reported-by: syzbot+c814aa406cfbf5f58583@syzkaller.appspotmail.com
First crash: 420d, last: 420d
▶ ▼ 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
linux-5.15 possible deadlock in kernfs_fop_write_iter 4 3 535d 631d 0/3 auto-obsoleted due to no activity on 2025/05/17 20:05
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

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
5.15.184-syzkaller #0 Not tainted
------------------------------------------------------
syz.6.737/8212 is trying to acquire lock:
ffff888062b69488 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e5/0x4c0 fs/kernfs/file.c:287

but task is already holding lock:
ffff888077372868 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x195/0xc40 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}:
       __mutex_lock_common+0x1eb/0x2390 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+0x195/0xc40 fs/splice.c:635
       do_splice_from fs/splice.c:767 [inline]
       do_splice+0xe65/0x1640 fs/splice.c:1079
       __do_splice fs/splice.c:1144 [inline]
       __do_sys_splice fs/splice.c:1350 [inline]
       __se_sys_splice+0x327/0x410 fs/splice.c:1332
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #6 (sb_writers#3){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1811 [inline]
       sb_start_write include/linux/fs.h:1881 [inline]
       file_start_write include/linux/fs.h:3042 [inline]
       lo_write_bvec+0x193/0x770 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:2235 [inline]
       loop_process_work+0x1d62/0x2480 drivers/block/loop.c:2275
       process_one_work+0x863/0x1000 kernel/workqueue.c:2310
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #5 ((work_completion)(&worker->work)){+.+.}-{0:0}:
       process_one_work+0x7bf/0x1000 kernel/workqueue.c:2286
       worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
       kthread+0x436/0x520 kernel/kthread.c:334
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #4 ((wq_completion)loop5){+.+.}-{0:0}:
       flush_workqueue+0x142/0x1380 kernel/workqueue.c:2830
       drain_workqueue+0xcf/0x380 kernel/workqueue.c:2995
       destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439
       __loop_clr_fd+0x234/0xb90 drivers/block/loop.c:1384
       blkdev_put_whole block/bdev.c:692 [inline]
       blkdev_put+0x53f/0x7d0 block/bdev.c:957
       btrfs_close_bdev fs/btrfs/volumes.c:1189 [inline]
       btrfs_close_one_device fs/btrfs/volumes.c:1210 [inline]
       close_fs_devices+0x48a/0x930 fs/btrfs/volumes.c:1253
       btrfs_close_devices+0xc2/0x500 fs/btrfs/volumes.c:1268
       close_ctree+0x75f/0x8c0 fs/btrfs/disk-io.c:4538
       generic_shutdown_super+0x130/0x300 fs/super.c:475
       kill_anon_super+0x36/0x70 fs/super.c:1089
       btrfs_kill_super+0x3d/0x50 fs/btrfs/super.c:2390
       deactivate_locked_super+0x93/0xf0 fs/super.c:335
       cleanup_mnt+0x418/0x4d0 fs/namespace.c:1143
       task_work_run+0x125/0x1a0 kernel/task_work.c:188
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop+0x10f/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+0x16/0x40 kernel/entry/common.c:307
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #3 (&lo->lo_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0x6a/0x100 drivers/block/loop.c:2056
       blkdev_get_whole+0x90/0x390 block/bdev.c:669
       blkdev_get_by_dev+0x2d0/0xa60 block/bdev.c:827
       blkdev_open+0x12d/0x2c0 block/fops.c:466
       do_dentry_open+0x7ff/0xf80 fs/open.c:826
       do_open fs/namei.c:3608 [inline]
       path_openat+0x2682/0x2f30 fs/namei.c:3742
       do_filp_open+0x1b3/0x3e0 fs/namei.c:3769
       do_sys_openat2+0x142/0x4a0 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+0x135/0x160 fs/open.c:1280
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #2 (&disk->open_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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+0x157/0xa60 block/bdev.c:820
       swsusp_check+0x9b/0x2a0 kernel/power/swap.c:1526
       software_resume+0xc6/0x3b0 kernel/power/hibernate.c:982
       resume_store+0xe4/0x130 kernel/power/hibernate.c:1184
       kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2172 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x712/0xd00 fs/read_write.c:594
       ksys_write+0x14d/0x250 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (system_transition_mutex/1){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 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/0x3b0 kernel/power/hibernate.c:937
       resume_store+0xe4/0x130 kernel/power/hibernate.c:1184
       kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2172 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x712/0xd00 fs/read_write.c:594
       ksys_write+0x14d/0x250 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 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 kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
       lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
       __mutex_lock_common+0x1eb/0x2390 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+0x1e5/0x4c0 fs/kernfs/file.c:287
       do_iter_readv_writev+0x497/0x600 fs/read_write.c:-1
       do_iter_write+0x205/0x7b0 fs/read_write.c:855
       iter_file_splice_write+0x65f/0xc40 fs/splice.c:689
       do_splice_from fs/splice.c:767 [inline]
       do_splice+0xe65/0x1640 fs/splice.c:1079
       __do_splice fs/splice.c:1144 [inline]
       __do_sys_splice fs/splice.c:1350 [inline]
       __se_sys_splice+0x327/0x410 fs/splice.c:1332
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 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.6.737/8212:
 #0: ffff88807f428460 (sb_writers#8){.+.+}-{0:0}, at: __do_splice fs/splice.c:1144 [inline]
 #0: ffff88807f428460 (sb_writers#8){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1350 [inline]
 #0: ffff88807f428460 (sb_writers#8){.+.+}-{0:0}, at: __se_sys_splice+0x327/0x410 fs/splice.c:1332
 #1: ffff888077372868 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x195/0xc40 fs/splice.c:635

stack backtrace:
CPU: 0 PID: 8212 Comm: syz.6.737 Not tainted 5.15.184-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 check_noncircular+0x274/0x310 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 kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 __mutex_lock_common+0x1eb/0x2390 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+0x1e5/0x4c0 fs/kernfs/file.c:287
 do_iter_readv_writev+0x497/0x600 fs/read_write.c:-1
 do_iter_write+0x205/0x7b0 fs/read_write.c:855
 iter_file_splice_write+0x65f/0xc40 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 do_splice+0xe65/0x1640 fs/splice.c:1079
 __do_splice fs/splice.c:1144 [inline]
 __do_sys_splice fs/splice.c:1350 [inline]
 __se_sys_splice+0x327/0x410 fs/splice.c:1332
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f3ab9e8d969
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:00007f3ab7cd4038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f3aba0b5080 RCX: 00007f3ab9e8d969
RDX: 0000000000000009 RSI: 0000000000000000 RDI: 0000000000000007
RBP: 00007f3ab9f0fab1 R08: 000000000000bfd1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f3aba0b5080 R15: 00007fff63573388
 </TASK>
set kvm_intel.dump_invalid_vmcs=1 to dump internal KVM state.
bridge0: port 2(bridge_slave_1) entered disabled state
device bridge_slave_1 left promiscuous mode
bridge0: port 2(bridge_slave_1) entered disabled state

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/01 09:33 linux-5.15.y 98f47d0e9b8c 3d2f584d .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.