Re: WARNING in __kernel_read

[Christoph Hellwig <hch@lst.de>]

On Mon, Jul 13, 2020 at 12:03:17AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:

This is not a crash, but a WARN_ON_ONCE, someone really needs to fix
syzbot to report this correctly.

The fix should be queued up by the 9p maintainers.

> 
> HEAD commit:    a581387e Merge tag 'io_uring-5.8-2020-07-10' of git://git...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13e730eb100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=66ad203c2bb6d8b
> dashboard link: https://syzkaller.appspot.com/bug?extid=d012ca3f813739c37c25
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e0222b100000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162a004f100000
> 
> The bug was bisected to:
> 
> commit 6209dd9132e8ea5545cffc84483841e88ea8cc5b
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Fri May 8 07:00:28 2020 +0000
> 
>     fs: implement kernel_read using __kernel_read
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=152d91fb100000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=172d91fb100000
> console output: https://syzkaller.appspot.com/x/log.txt?x=132d91fb100000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+d012ca3f813739c37c25@syzkaller.appspotmail.com
> Fixes: 6209dd9132e8 ("fs: implement kernel_read using __kernel_read")
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5 at fs/read_write.c:427 __kernel_read+0x41d/0x4d0 fs/read_write.c:427
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.8.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events p9_read_work
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x18f/0x20d lib/dump_stack.c:118
>  panic+0x2e3/0x75c kernel/panic.c:231
>  __warn.cold+0x20/0x45 kernel/panic.c:600
>  report_bug+0x1bd/0x210 lib/bug.c:198
>  handle_bug+0x38/0x90 arch/x86/kernel/traps.c:235
>  exc_invalid_op+0x13/0x40 arch/x86/kernel/traps.c:255
>  asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:542
> RIP: 0010:__kernel_read+0x41d/0x4d0 fs/read_write.c:427
> Code: fd ff ff e8 75 19 b6 ff 45 31 c9 45 31 c0 b9 01 00 00 00 4c 89 f2 89 ee 4c 89 ef e8 5d 22 12 00 e9 46 ff ff ff e8 53 19 b6 ff <0f> 0b 49 c7 c4 ea ff ff ff e9 11 fe ff ff 4c 89 f7 e8 2d 76 f5 ff
> RSP: 0018:ffffc90000cbfbc8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffff8880a9786ac0 RCX: ffffffff81bd9ac4
> RDX: ffff8880a95a2140 RSI: ffffffff81bd9e3d RDI: 0000000000000005
> RBP: ffff888096bc8060 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 1ffffffff1829bdd R12: 00000000081d801e
> R13: ffffc90000cbfc98 R14: ffff8880a9786b44 R15: 0000000000000007
>  kernel_read+0x52/0x70 fs/read_write.c:457
>  p9_fd_read net/9p/trans_fd.c:263 [inline]
>  p9_read_work+0x2ac/0xff0 net/9p/trans_fd.c:298
>  process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
>  kthread+0x3b5/0x4a0 kernel/kthread.c:291
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
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> 
> syzbot will keep track of this bug report. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
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