linux-kernel - Re: [PATCH 2/3] FS-Cache: Reduce cookie ref count if submit fails.

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Message-ID: <17620.1407847665@warthog.procyon.org.uk>
Date:	Tue, 12 Aug 2014 13:47:45 +0100
From:	David Howells <dhowells@...hat.com>
To:	Milosz Tanski <milosz@...in.com>
Cc:	dhowells@...hat.com,
	"linux-cachefs@...hat.com" <linux-cachefs@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, NeilBrown <neilb@...e.de>,
	Shantanu Goel <sgoel01@...oo.com>
Subject: Re: [PATCH 2/3] FS-Cache: Reduce cookie ref count if submit fails.

Milosz Tanski <milosz@...in.com> wrote:

> The honest answer is I don't know if it know if needs to be unlocked
> before or after. I saw a same pattern with unlocking order inside of
> __fscache_attr_changed in the failure case.

Following the enomem label, I'm calling fscache_unuse_cookie() which does this
without holding the lock in the same function.

I don't think the lock is required because:

 (1) We hold a ref on cookie->n_active so the cookie cannot go away until we
     release it, so calling __fscache_unuse_cookie() without the lock held
     should be fine.

 (2) wake_up_atomic_t() does not access cookie->n_active.  The address is
     merely needed as a key for the waiters to match on.

David
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