Re: fs: GPF in locked_inode_to_wb_and_lock_list

From: Dmitry Vyukov
Date: Thu Apr 21 2016 - 06:01:04 EST

On Thu, Apr 21, 2016 at 11:45 AM, Andrey Ryabinin
<ryabinin.a.a@xxxxxxxxx> wrote:
> 2016-04-21 11:35 GMT+03:00 Dmitry Vyukov <dvyukov@xxxxxxxxxx>:
>> ffffffff818884dd: 48 8b 03 mov (%rbx),%rax
>> So whatever load "&wb->bdi->wb" produces is a NULL deref. (is it wb
>> that is NULL?)
> Yes it's NULL wb, because there is only one load:
> mov (%rbx),%rax => rax = wb->bdi
> add $0x50,%rax => rax = &bdi->wb

I bet that wb becomes NULL on the second iteration of the loop. The
loop loops in case of a race with another thread, so it would also
explain why it is difficult to reproduce.

Tejun, does it make any sense to you?