linux-kernel - Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an atomic_long

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Message-ID: <875znxkpj0.fsf@suse.com>
Date:   Sat, 20 Jul 2019 10:45:39 +0100
From:   Luis Henriques <lhenriques@...e.com>
To:     "Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:     "Waiman Long" <longman@...hat.com>,
        "Borislav Petkov" <bp@...en8.de>,
        "Will Deacon" <will.deacon@....com>,
        "huang ying" <huang.ying.caritas@...il.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "the arch\/x86 maintainers" <x86@...nel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Tim Chen" <tim.c.chen@...ux.intel.com>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Davidlohr Bueso" <dave@...olabs.net>,
        "Linux List Kernel Mailing" <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Jeff Layton" <jlayton@...nel.org>
Subject: Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an atomic_long_t

Luis Henriques <lhenriques@...e.com> writes:

> Luis Henriques <lhenriques@...e.com> writes:
>
>> "Linus Torvalds" <torvalds@...ux-foundation.org> writes:
>>
>>> On Fri, Jul 19, 2019 at 12:32 PM Waiman Long <longman@...hat.com> wrote:
>>>>
>>>> This patch shouldn't change the behavior of the rwsem code. The code
>>>> only access data within the rw_semaphore structures. I don't know why it
>>>> will cause a KASAN error. I will have to reproduce it and figure out
>>>> exactly which statement is doing the invalid access.
>>>
>>> The stack traces should show line numbers if you run them through
>>> scripts/decode_stacktrace.sh.
>>>
>>> You need to have debug info enabled for that, though.
>>>
>>> Luis?
>>>
>>>              Linus
>>
>> Yep, sure.  And I should have done this in the initial report.  It's a
>> different trace, I had to recompile the kernel.
>>
>> (I'm also adding Jeff to the CC list.)
>>
>
> Ah, and I also managed to reproduce this on btrfs so I guess this rules
> out a bug in the filesystem code.

Just another detail (before I go completely offline until tomorrow
evening): in the btrfs case I'm seeing the bug on the
rwsem_down_read_slowpath path, not on rwsem_down_write_slowpath.  But it
seems to be on the same place (i.e. rwsem_can_spin_on_owner).

Cheers,
-- 
Luis