linux-kernel - Re: [PATCH] slub: Fix sysfs circular locking dependency

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Date:	Mon, 10 Jan 2011 10:15:15 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Pekka Enberg <penberg@...nel.org>
cc:	Bart Van Assche <bvanassche@....org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

New patch that just covers the slub changes.

Subject: slub: Avoid use of slub_lock in show_slab_objects()

The purpose of the locking is to prevent removal and additions
of nodes when statistics are gathered for a slab cache. So we
need to avoid racing with memory hotplug functionality.

It is enough to take the memory hotplug locks there instead
of the slub_lock.

online_pages() currently does not acquire the memory_hotplug
lock. Another patch will be submitted by the memory hotplug
authors to take the memory hotplug lock and describe the
uses of the memory hotplug lock to protect against
adding and removal of nodes from non hotplug data structures.

Signed-off-by: Christoph Lameter <cl@...ux.com>

---
 mm/memory_hotplug.c |   17 +++++++++++------
 mm/slub.c           |    4 ++--
 2 files changed, 13 insertions(+), 8 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2011-01-10 09:02:08.000000000 -0600
+++ linux-2.6/mm/slub.c	2011-01-10 10:10:46.000000000 -0600
@@ -3781,7 +3781,7 @@ static ssize_t show_slab_objects(struct
 		}
 	}

-	down_read(&slub_lock);
+	lock_memory_hotplug();
 #ifdef CONFIG_SLUB_DEBUG
 	if (flags & SO_ALL) {
 		for_each_node_state(node, N_NORMAL_MEMORY) {
@@ -3822,7 +3822,7 @@ static ssize_t show_slab_objects(struct
 			x += sprintf(buf + x, " N%d=%lu",
 					node, nodes[node]);
 #endif
-	up_read(&slub_lock);
+	unlock_memory_hotplug();
 	kfree(nodes);
 	return x + sprintf(buf + x, "\n");
 }

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