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

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Message-ID: <2ed44afa-4528-a785-f188-2daf24343f97@redhat.com>
Date:   Fri, 19 Jul 2019 15:32:10 -0400
From:   Waiman Long <longman@...hat.com>
To:     Luis Henriques <lhenriques@...e.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an
 atomic_long_t

On 7/19/19 2:45 PM, Luis Henriques wrote:
> On Mon, May 20, 2019 at 04:59:12PM -0400, Waiman Long wrote:
>> The rwsem->owner contains not just the task structure pointer, it also
>> holds some flags for storing the current state of the rwsem. Some of
>> the flags may have to be atomically updated. To reflect the new reality,
>> the owner is now changed to an atomic_long_t type.
>>
>> New helper functions are added to properly separate out the task
>> structure pointer and the embedded flags.
> I started seeing KASAN use-after-free with current master, and a bisect
> showed me that this commit 94a9717b3c40 ("locking/rwsem: Make
> rwsem->owner an atomic_long_t") was the problem.  Does it ring any
> bells?  I can easily reproduce it with xfstests (generic/464).
>
> Cheers,
> --
> Luís

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.

Thanks,
Longman