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From: Tahsin Erdogan <tahsin@google.com>
Date: Mon, 27 Mar 2017 11:29:18 -0700
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Subject: Re: [PATCH] blkcg: allocate struct blkcg_gq outside request queue spinlock
To: Julia Lawall <julia.lawall@lip6.fr>
Cc: Tejun Heo <tj@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, David Rientjes <rientjes@google.com>,
        linux-kernel@vger.kernel.org
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On Sun, Mar 26, 2017 at 3:54 AM, Julia Lawall <julia.lawall@lip6.fr> wrote:
> Is an unlock needed before line 848?  Or does blkg_lookup_check take care
> of it?

Unlock is not needed. On success, function returns with locks held.
It is documented at line 805:

"... This function returns with RCU read
 * lock and queue lock held and must be paired with blkg_conf_finish()."