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 6:51 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200115065055.GA21219@lst.de \
--to=hch@lst.de \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=stable@vger.kernel.org \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.