linux-kernel - Re: [patch] nfs: fix locking in nfs/inode.c in nfs_free_open

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Message-Id: <1185384502.6585.97.camel@localhost>
Date:	Wed, 25 Jul 2007 13:28:22 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Christian Krafft <krafft@...ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch] nfs: fix locking in nfs/inode.c in
	nfs_free_open_context

On Wed, 2007-07-25 at 17:08 +0200, Christian Krafft wrote:

> Obviously the locking code in nfs_free_open_context is wrong.
> Checking the list for entries and removing the entry should be an atomic operation.

Wrong. It is quite safe to test the structure member ctx->list for
emptiness outside the spinlock because we have an explicit guarantee
that nobody else has a reference to this structure, plus the
atomic_dec_and_test() in kref_put() has acted as a memory barrier for
us.

> Also list_del_init should be used, because list_del will leave the empty list in
> an undefined condition.

Huh? We're freeing the context. It will _never_ _ever_ _ever_ be used
again. If anything tries to use ctx->list after this, then that is a
major bug.

Patch rejected...

Trond

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