Re: [syzbot] WARNING in __cleanup_sighand

[Eric Biggers]

On Sun, Jan 16, 2022 at 04:05:24PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    79e06c4c4950 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1285ed28700000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=afd3ce8cd5cf174b
> dashboard link: https://syzkaller.appspot.com/bug?extid=985a662ba46639a7897f
> 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+985a662ba46639a7897f@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 3640 at kernel/sched/wait.c:245 __wake_up_pollfree+0x1c7/0x1d0 kernel/sched/wait.c:246
> Modules linked in:
> CPU: 0 PID: 3640 Comm: syz-executor.3 Not tainted 5.16.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__wake_up_pollfree+0x1c7/0x1d0 kernel/sched/wait.c:245
> Code: 0d 00 00 c6 44 08 0f 00 65 48 8b 04 25 28 00 00 00 48 3b 84 24 a0 00 00 00 75 13 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 <0f> 0b eb a7 e8 60 3e b0 08 55 41 57 41 56 41 55 41 54 53 48 83 ec
> RSP: 0018:ffffc900028cf760 EFLAGS: 00010097
> RAX: ffff88801ec1b130 RBX: 0000000000000046 RCX: dffffc0000000000
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
> RBP: ffffc900028cf848 R08: dffffc0000000000 R09: ffffed100850025a
> R10: ffffed100850025a R11: 0000000000000000 R12: 0000000000000000
> R13: ffffc900028cf7a0 R14: 1ffff92000519ef4 R15: ffff888042801308
> FS:  0000555556549400(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fed83b131b8 CR3: 000000004a82a000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 000000000000802e DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __cleanup_sighand+0x48/0xa0 kernel/fork.c:1590
>  __exit_signal kernel/exit.c:159 [inline]
>  release_task+0x115f/0x15d0 kernel/exit.c:200
>  wait_task_zombie kernel/exit.c:1114 [inline]
>  wait_consider_task+0x1995/0x2fb0 kernel/exit.c:1341
>  do_wait_thread kernel/exit.c:1404 [inline]
>  do_wait+0x291/0x9d0 kernel/exit.c:1521
>  kernel_wait4+0x2a3/0x3c0 kernel/exit.c:1684
>  __do_sys_wait4 kernel/exit.c:1712 [inline]
>  __se_sys_wait4 kernel/exit.c:1708 [inline]
>  __x64_sys_wait4+0x130/0x1e0 kernel/exit.c:1708
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f2aff29e487
> Code: 89 7c 24 10 48 89 4c 24 18 e8 35 50 02 00 4c 8b 54 24 18 8b 54 24 14 41 89 c0 48 8b 74 24 08 8b 7c 24 10 b8 3d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 89 44 24 10 e8 65 50 02 00 8b 44
> RSP: 002b:00007ffeabee34f0 EFLAGS: 00000293 ORIG_RAX: 000000000000003d
> RAX: ffffffffffffffda RBX: 0000000000000932 RCX: 00007f2aff29e487
> RDX: 0000000040000001 RSI: 00007ffeabee357c RDI: 00000000ffffffff
> RBP: 00007ffeabee357c R08: 0000000000000000 R09: 0000000000000010
> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000032
> R13: 00000000000af2e3 R14: 0000000000000009 R15: 00007ffeabee35e0
>  </TASK>
> 
> 

This is probably caused by io_uring not handling POLLFREE notifications,
i.e. this is probably a duplicate of the previous syzbot report
https://lore.kernel.org/lkml/000000000000c9a3fb05d4d787a3@xxxxxxxxxx/T/#u
("WARNING in signalfd_cleanup").  It's impossible to be certain without a
reproducer, but based on the console output here, some of the programs that
syzkaller executed use io_uring.  So it's at least plausible.

- Eric