Re: WARNING in rcu_irq_exit

[Vitaly Kuznetsov]

syzbot <syzbot+c116bcba868f8148cd3e@xxxxxxxxxxxxxxxxxxxxxxxxx> writes:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    47ec5303 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17228c62900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e0c783f658542f35
> dashboard link: https://syzkaller.appspot.com/bug?extid=c116bcba868f8148cd3e
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>
> 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+c116bcba868f8148cd3e@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> device lo entered promiscuous mode
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 29030 at kernel/rcu/tree.c:772 rcu_irq_exit+0x19/0x20 kernel/rcu/tree.c:773
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 29030 Comm: syz-executor.2 Not tainted 5.8.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1f0/0x31e lib/dump_stack.c:118
>  panic+0x264/0x7a0 kernel/panic.c:231
>  __warn+0x227/0x250 kernel/panic.c:600
>  report_bug+0x1b1/0x2e0 lib/bug.c:198
>  handle_bug+0x42/0x80 arch/x86/kernel/traps.c:235
>  exc_invalid_op+0x16/0x40 arch/x86/kernel/traps.c:255
>  asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
> RIP: 0010:rcu_irq_exit+0x19/0x20 kernel/rcu/tree.c:773
> Code: 0b c3 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 83 3d fd fb 68 01 00 74 0b 65 8b 05 50 00 dc 77 85 c0 75 05 e9 07 ff ff ff <0f> 0b e9 00 ff ff ff 41 56 53 83 3d da fb 68 01 00 74 0f 65 8b 05
> RSP: 0018:ffffc90001806e70 EFLAGS: 00010002
> RAX: 0000000000000001 RBX: 0000000000000082 RCX: 0000000000040000
> RDX: ffffc9000da6b000 RSI: 0000000000003173 RDI: 0000000000003174
> RBP: ffff8880a2ce9fa8 R08: ffffffff817a9064 R09: ffffed1015d26cf5
> R10: ffffed1015d26cf5 R11: 0000000000000000 R12: dffffc0000000000
> R13: 000000000000003c R14: dffffc0000000000 R15: 000000000000003c
>  rcu_irq_exit_irqson+0x80/0x110 kernel/rcu/tree.c:827
...

Chances are this is fixed by Tglx' 

commit 87fa7f3e98a1310ef1ac1900e7ee7f9610a038bc
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date:   Wed Jul 8 21:51:54 2020 +0200

    x86/kvm: Move context tracking where it belongs

(in kvm/next currently).

See also: https://lore.kernel.org/kvm/ece36eb1-253a-8ec6-c183-309c10bb35d5@xxxxxxxxxx/
which was confirmed to be fixed by the above mentioned commit.

-- 
Vitaly