linux-kernel - [PATCH 1/1] vmalloc: purge_fragmented_blocks: Acquire spinlock before reading vmap

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Date:	Thu,  8 Dec 2011 12:32:12 +0530
From:	Kautuk Consul <consul.kautuk@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	David Vrabel <david.vrabel@...rix.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Kautuk Consul <consul.kautuk@...il.com>
Subject: [PATCH 1/1] vmalloc: purge_fragmented_blocks: Acquire spinlock before reading vmap_block

The purge_fragmented_blocks will loop over all vmap_blocks in the
vmap_block_queue to create the purge list.
Currently, the code in the loop does not acquire the &vb->lock before
reading the vb->free and vb->dirty.

Due to this, there might be a possibility of vb->free and vb->dirty being
changed in parallel which could lead to the current vmap_block not being
selected for purging.

Changing the code to acquire this spinlock before the check for vb->free
and vb->dirty.

Signed-off-by: Kautuk Consul <consul.kautuk@...il.com>
---
 mm/vmalloc.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3231bf3..2228971 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -855,11 +855,14 @@ static void purge_fragmented_blocks(int cpu)
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(vb, &vbq->free, free_list) {
+		spin_lock(&vb->lock);
 
-		if (!(vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS))
+		if (!(vb->free + vb->dirty == VMAP_BBMAP_BITS &&
+			  vb->dirty != VMAP_BBMAP_BITS)) {
+			spin_unlock(&vb->lock);
 			continue;
+		}
 
-		spin_lock(&vb->lock);
 		if (vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS) {
 			vb->free = 0; /* prevent further allocs after releasing lock */
 			vb->dirty = VMAP_BBMAP_BITS; /* prevent purging it again */
-- 
1.7.6

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