From 810ecfa765f8be20c8d9c468885b3403a2232d2f Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Wed, 9 Jan 2013 08:05:13 -0800
Subject: [PATCH] blkcg: make blkcg_print_blkgs() grab q locks instead of blkcg
 lock

Instead of holding blkcg->lock while walking ->blkg_list and executing
prfill(), RCU walk ->blkg_list and hold the blkg's queue lock while
executing prfill().  This makes prfill() implementations easier as
stats are mostly protected by queue lock.

This will be used to implement hierarchical stats.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
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