From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: David Howells <dhowells@redhat.com>
Cc: gregkh@linux-foundation.org,
Kiran Kumar Modukuri <kiran.modukuri@gmail.com>,
viro@zeniv.linux.org.uk, sandeen@redhat.com,
linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] fscache: Fix race in fscache_op_complete() due to split atomic_sub & read
Date: Wed, 17 Oct 2018 17:11:34 +0200 [thread overview]
Message-ID: <20181017151134.GA8966@andrea> (raw)
In-Reply-To: <153978621809.8478.2198040871218302573.stgit@warthog.procyon.org.uk>
Hi David,
On Wed, Oct 17, 2018 at 03:23:38PM +0100, David Howells wrote:
> From: kiran.modukuri <kiran.modukuri@gmail.com>
>
> The code in fscache_retrieval_complete is using atomic_sub followed by an
> atomic_read:
>
> atomic_sub(n_pages, &op->n_pages);
> if (atomic_read(&op->n_pages) <= 0)
> fscache_op_complete(&op->op, true);
>
> This causes two threads doing a decrement of n_pages to race with each
> other seeing the op->refcount 0 at same time - and they end up calling
> fscache_op_complete() in both the threads leading to an assertion failure.
>
> Fix this by using atomic_sub_return() instead of two calls.
Seems a case for atomic_sub_return_relaxed()... why not?
Andrea
next prev parent reply other threads:[~2018-10-17 23:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-17 14:23 [PATCH 0/4] FS-Cache: Miscellaneous fixes David Howells
2018-10-17 14:23 ` [PATCH 1/4] cachefiles: fix the race between cachefiles_bury_object() and rmdir(2) David Howells
2018-10-17 14:23 ` [PATCH 2/4] fscache: Fix race in fscache_op_complete() due to split atomic_sub & read David Howells
2018-10-17 15:11 ` Andrea Parri [this message]
2018-10-17 15:32 ` David Howells
2018-10-17 16:48 ` Andrea Parri
2018-11-26 16:26 ` David Howells
2018-11-26 16:56 ` Andrea Parri
2018-11-28 14:43 ` David Howells
2018-11-28 20:45 ` Andrea Parri
2018-10-17 14:23 ` [PATCH 3/4] fscache: Fix incomplete initialisation of inline key space David Howells
2018-10-17 14:23 ` [PATCH 4/4] fscache: Fix out of bound read in long cookie keys David Howells
2018-10-18 10:03 ` [PATCH 0/4] FS-Cache: Miscellaneous fixes Greg KH
-- strict thread matches above, loose matches on Subject: below --
2018-10-17 14:16 David Howells
2018-10-17 14:17 ` [PATCH 2/4] fscache: Fix race in fscache_op_complete() due to split atomic_sub & read David Howells
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