[syzbot] INFO: task hung in io_uring_release (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bc491fb12513 Merge tag 'fixes-2021-12-22' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165b1a5db00000
kernel config: https://syzkaller.appspot.com/x/.config?x=6104739ac5f067ea
dashboard link: https://syzkaller.appspot.com/bug?extid=f4dee1c474a6e3f68100
compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f4dee1...@syzkaller.appspotmail.com

INFO: task syz-executor.2:8284 blocked for more than 143 seconds.
Not tainted 5.16.0-rc6-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2 state:D stack:26704 pid: 8284 ppid: 3729 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:4972 [inline]
__schedule+0xb72/0x1460 kernel/sched/core.c:6253
schedule+0x12b/0x1f0 kernel/sched/core.c:6326
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6385
__mutex_lock_common+0xd1f/0x2590 kernel/locking/mutex.c:680
__mutex_lock kernel/locking/mutex.c:740 [inline]
mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:792
io_ring_ctx_wait_and_kill+0xa0/0x36a fs/io_uring.c:9565
io_uring_release+0x59/0x63 fs/io_uring.c:9594
__fput+0x3fc/0x870 fs/file_table.c:280
task_work_run+0x146/0x1c0 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
exit_to_user_mode_prepare+0x209/0x220 kernel/entry/common.c:207
__syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300
do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f7b18378adb
RSP: 002b:00007ffe8c741150 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00007f7b18378adb
RDX: 0000001b2cc20000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f7b184da960 R08: 0000000000000000 R09: 0000000000000010
R10: 00007ffe8c76b0b8 R11: 0000000000000293 R12: 000000000007cb81
R13: 00007f7b184dfb50 R14: 00007f7b184d9370 R15: 0000000000000005
</TASK>
INFO: task syz-executor.2:8285 blocked for more than 143 seconds.
Not tainted 5.16.0-rc6-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2 state:D stack:23728 pid: 8285 ppid: 3729 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:4972 [inline]
__schedule+0xb72/0x1460 kernel/sched/core.c:6253
schedule+0x12b/0x1f0 kernel/sched/core.c:6326
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6385
__mutex_lock_common+0xd1f/0x2590 kernel/locking/mutex.c:680
__mutex_lock kernel/locking/mutex.c:740 [inline]
mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:792
io_uring_del_tctx_node+0xe4/0x2a9 fs/io_uring.c:9777
io_uring_clean_tctx+0x192/0x1d5 fs/io_uring.c:9793
io_uring_cancel_generic+0x629/0x671 fs/io_uring.c:9884
io_uring_files_cancel include/linux/io_uring.h:16 [inline]
do_exit+0x281/0x24f0 kernel/exit.c:787
do_group_exit+0x168/0x2d0 kernel/exit.c:929
get_signal+0x1740/0x2120 kernel/signal.c:2852
arch_do_signal_or_restart+0x9c/0x730 arch/x86/kernel/signal.c:868
handle_signal_work kernel/entry/common.c:148 [inline]
exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
exit_to_user_mode_prepare+0x191/0x220 kernel/entry/common.c:207
__syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300
do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f7b183c5e99
RSP: 002b:00007f7b16d3b218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f7b184d8f68 RCX: 00007f7b183c5e99
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f7b184d8f68
RBP: 00007f7b184d8f60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7b184d8f6c
R13: 00007ffe8c7410ef R14: 00007f7b16d3b300 R15: 0000000000022000
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
#0: ffffffff8cb1de00 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by getty/3280:
#0: ffff88807f219098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
#1: ffffc90002b962e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6c5/0x1c60 drivers/tty/n_tty.c:2113
1 lock held by syz-executor.2/8284:
#0: ffff88801de6e0a8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_ring_ctx_wait_and_kill+0xa0/0x36a fs/io_uring.c:9565
1 lock held by syz-executor.2/8285:
#0: ffff88801de6e0a8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_uring_del_tctx_node+0xe4/0x2a9 fs/io_uring.c:9777
1 lock held by syz-executor.2/8302:
#0: ffff88801de6e0a8 (&ctx->uring_lock){+.+.}-{3:3}, at: tctx_task_work+0x2e5/0x560 fs/io_uring.c:2242

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 27 Comm: khungtaskd Not tainted 5.16.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1dc/0x2d8 lib/dump_stack.c:106
nmi_cpu_backtrace+0x45f/0x490 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x16a/0x280 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:210 [inline]
watchdog+0xc82/0xcd0 kernel/hung_task.c:295
kthread+0x468/0x490 kernel/kthread.c:327
ret_from_fork+0x1f/0x30
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 1090 Comm: kworker/u4:5 Not tainted 5.16.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: phy4 ieee80211_iface_work
RIP: 0010:unwind_next_frame+0x42f/0x1fc0 arch/x86/kernel/unwind_orc.c:456
Code: 03 42 8a 04 30 84 c0 0f 85 0c 16 00 00 c6 03 01 48 c7 c5 80 80 6b 8a 4c 8d 7d 04 48 8d 5d 05 4d 89 fc 49 c1 ec 03 43 8a 04 34 <84> c0 0f 85 8e 15 00 00 48 89 d8 48 c1 e8 03 42 8a 04 30 84 c0 0f
RSP: 0018:ffffc90004ecf0c0 EFLAGS: 00000a06
RAX: 0000000000000000 RBX: ffffffff8efe0283 RCX: ffffffff8e677054
RDX: ffffffff8efe027e RSI: ffffffff89835db7 RDI: ffffffff813ab429
RBP: ffffffff8efe027e R08: 0000000000000001 R09: ffffc90004ecf270
R10: fffff520009d9e3c R11: 0000000000000000 R12: 1ffffffff1dfc050
R13: ffffffff8e677050 R14: dffffc0000000000 R15: ffffffff8efe0282
FS: 0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c015a2e2c8 CR3: 000000000c88e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
arch_stack_walk+0x112/0x140 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x11b/0x1e0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc+0xdc/0x110 mm/kasan/common.c:513
kasan_kmalloc include/linux/kasan.h:269 [inline]
__kmalloc+0x253/0x380 mm/slub.c:4423
kmalloc include/linux/slab.h:595 [inline]
kzalloc+0x1d/0x30 include/linux/slab.h:724
cfg80211_inform_single_bss_frame_data net/wireless/scan.c:2397 [inline]
cfg80211_inform_bss_frame_data+0x427/0x1f40 net/wireless/scan.c:2458
ieee80211_bss_info_update+0x75b/0xbe0 net/mac80211/scan.c:190
ieee80211_rx_bss_info net/mac80211/ibss.c:1119 [inline]
ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1610 [inline]
ieee80211_ibss_rx_queued_mgmt+0x1690/0x2b30 net/mac80211/ibss.c:1639
ieee80211_iface_process_skb net/mac80211/iface.c:1468 [inline]
ieee80211_iface_work+0x709/0xc90 net/mac80211/iface.c:1522
process_one_work+0x853/0x1140 kernel/workqueue.c:2298
worker_thread+0xac1/0x1320 kernel/workqueue.c:2445
kthread+0x468/0x490 kernel/kthread.c:327
ret_from_fork+0x1f/0x30
</TASK>
----------------
Code disassembly (best guess):
0: 03 42 8a add -0x76(%rdx),%eax
3: 04 30 add $0x30,%al
5: 84 c0 test %al,%al
7: 0f 85 0c 16 00 00 jne 0x1619
d: c6 03 01 movb $0x1,(%rbx)
10: 48 c7 c5 80 80 6b 8a mov $0xffffffff8a6b8080,%rbp
17: 4c 8d 7d 04 lea 0x4(%rbp),%r15
1b: 48 8d 5d 05 lea 0x5(%rbp),%rbx
1f: 4d 89 fc mov %r15,%r12
22: 49 c1 ec 03 shr $0x3,%r12
26: 43 8a 04 34 mov (%r12,%r14,1),%al
* 2a: 84 c0 test %al,%al <-- trapping instruction
2c: 0f 85 8e 15 00 00 jne 0x15c0
32: 48 89 d8 mov %rbx,%rax
35: 48 c1 e8 03 shr $0x3,%rax
39: 42 8a 04 30 mov (%rax,%r14,1),%al
3d: 84 c0 test %al,%al
3f: 0f .byte 0xf


---
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[Pavel Begunkov]

On 12/27/21 19:12, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: bc491fb12513 Merge tag 'fixes-2021-12-22' of git://git.ker..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=165b1a5db00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=6104739ac5f067ea
> dashboard link: https://syzkaller.appspot.com/bug?extid=f4dee1c474a6e3f68100
> compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f4dee1...@syzkaller.appspotmail.com

Neither io_uring_release() nor io_uring_del_tctx_node() can take
->uring_lock and so hung. Apparently, the lock is held by

1 lock held by syz-executor.2/8302:
#0: ffff88801de6e0a8 (&ctx->uring_lock){+.+.}-{3:3}, at: tctx_task_work+0x2e5/0x560 fs/io_uring.c:2242

The most likely scenario is that some lower layer doesn't honour
NOWAIT/NOBLOCK flags/etc. E.g. I'd guess it can happen with
io_uring using O_NONBLOCK pipes.

Also possible that tctx_task_work() screwed locking somehow, but
it's 5.16 and related bits shouldn't have been changed for a couple
of releases and so less likely.

Would be lovely to find a repro and/or see what ops were issued/etc.

[...]
--
Pavel Begunkov

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.