Re: WARNING in io_uring_flush

[Pavel Begunkov <asml.silence@gmail.com>]

On 15/01/2021 15:57, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    14662050 Merge tag 'linux-kselftest-fixes-5.11-rc4' of git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a09ed0d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c066f800cf2824be
> dashboard link: https://syzkaller.appspot.com/bug?extid=a32b546d58dde07875a1
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 
> 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+a32b546d58dde07875a1@syzkaller.appspotmail.com

I know a case how it can happen, and if that's the only way then this
is a false positive. I'll put up a patch and we'll if syzbot will
trigger it again.

> 
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 11100 at fs/io_uring.c:9096 io_uring_flush+0x326/0x3a0 fs/io_uring.c:9096
> Modules linked in:
> CPU: 1 PID: 11100 Comm: syz-executor.3 Not tainted 5.11.0-rc3-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:io_uring_flush+0x326/0x3a0 fs/io_uring.c:9096
> Code: e9 58 fe ff ff e8 6a 21 9b ff 49 c7 84 24 a0 00 00 00 00 00 00 00 e9 aa fe ff ff e8 44 9c dd ff e9 91 fd ff ff e8 4a 21 9b ff <0f> 0b e9 51 ff ff ff e8 3e 9c dd ff e9 06 fd ff ff 4c 89 f7 e8 31
> RSP: 0018:ffffc90000fd7aa0 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff8880758de140 RSI: ffffffff81d7aac6 RDI: 0000000000000003
> RBP: ffff8880264d8500 R08: 0000000000000000 R09: 0000000028eda801
> R10: ffffffff81d7aa15 R11: 0000000000000000 R12: ffff888035f73000
> R13: ffff888028eda801 R14: ffff888035f73040 R15: ffff888035f730d0
> FS:  0000000000000000(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f16cd441710 CR3: 000000006924f000 CR4: 00000000001506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  filp_close+0xb4/0x170 fs/open.c:1280
>  close_files fs/file.c:401 [inline]
>  put_files_struct fs/file.c:416 [inline]
>  put_files_struct+0x1cc/0x350 fs/file.c:413
>  exit_files+0x7e/0xa0 fs/file.c:433
>  do_exit+0xc22/0x2ae0 kernel/exit.c:820
>  do_group_exit+0x125/0x310 kernel/exit.c:922
>  get_signal+0x3e9/0x20a0 kernel/signal.c:2770
>  arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:811
>  handle_signal_work kernel/entry/common.c:147 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
>  exit_to_user_mode_prepare+0x148/0x250 kernel/entry/common.c:201
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45e219
> Code: Unable to access opcode bytes at RIP 0x45e1ef.
> RSP: 002b:00007f49d69f3c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffe0 RBX: 0000000000000006 RCX: 000000000045e219
> RDX: ffffffffffffffef RSI: 0000000020d7cfcb RDI: 0000000000000007
> RBP: 000000000119bfd8 R08: 0000000000000000 R09: 00000000ffffffd8
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119bf8c
> R13: 00007fff13b97d2f R14: 00007f49d69f49c0 R15: 000000000119bf8c
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 

-- 
Pavel Begunkov