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

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Date:	Wed, 5 Jan 2011 11:10:47 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	David Rientjes <rientjes@...gle.com>
cc:	Pekka Enberg <penberg@...nel.org>, linux-kernel@...r.kernel.org,
	Bart Van Assche <bart.vanassche@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] slub: Fix sysfs circular locking dependency

How about this solution? In the common case of kernels without hotplug
support there will be no locking at all.


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.


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

---
 mm/slub.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2011-01-05 09:55:34.000000000 -0600
+++ linux-2.6/mm/slub.c	2011-01-05 09:56:27.000000000 -0600
@@ -3821,7 +3821,7 @@ 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) {
@@ -3862,7 +3862,7 @@ 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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