linux-kernel - Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER

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Message-ID: <20200115153730.GO2827@hirez.programming.kicks-ass.net>
Date:   Wed, 15 Jan 2020 16:37:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on
 RWSEM_OWNER_UNKNOWN

On Wed, Jan 15, 2020 at 07:50:55AM +0100, Christoph Hellwig wrote:
> On Tue, Jan 14, 2020 at 02:03:03PM -0500, Waiman Long wrote:
> > The commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer
> > optimistically spin on owner") will allow a recently woken up waiting
> > writer to spin on the owner. Unfortunately, if the owner happens to be
> > RWSEM_OWNER_UNKNOWN, the code will incorrectly spin on it leading to a
> > kernel crash. This is fixed by passing the proper non-spinnable bits
> > to rwsem_spin_on_owner() so that RWSEM_OWNER_UNKNOWN will be treated
> > as a non-spinnable target.
> > 
> > Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner")
> > 
> > Reported-by: Christoph Hellwig <hch@....de>
> > Signed-off-by: Waiman Long <longman@...hat.com>
> 
> This survives all the tests that showed the problems with the original
> code:
> 
> Tested-by: Christoph Hellwig <hch@....de>

Thanks!