From: Christoph Hellwig <hch@lst.de>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
stable@vger.kernel.org
Subject: Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN
Date: Wed, 15 Jan 2020 07:50:55 +0100 [thread overview]
Message-ID: <20200115065055.GA21219@lst.de> (raw)
In-Reply-To: <20200114190303.5778-1-longman@redhat.com>
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@lst.de>
> Signed-off-by: Waiman Long <longman@redhat.com>
This survives all the tests that showed the problems with the original
code:
Tested-by: Christoph Hellwig <hch@lst.de>
> if ((wstate == WRITER_HANDOFF) &&
> - (rwsem_spin_on_owner(sem, 0) == OWNER_NULL))
> + rwsem_spin_on_owner(sem, RWSEM_NONSPINNABLE) == OWNER_NULL)
Nit: the inner braces in the first half of the conditional aren't required
either.
next prev parent reply other threads:[~2020-01-15 6:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 19:03 [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN Waiman Long
2020-01-15 6:50 ` Christoph Hellwig [this message]
2020-01-15 14:27 ` Waiman Long
2020-01-15 15:16 ` David Laight
2020-01-15 15:47 ` Waiman Long
2020-01-15 16:01 ` David Laight
2020-01-15 15:28 ` Waiman Long
2020-01-15 15:37 ` Peter Zijlstra
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