linux-kernel - [PATCH] staging: zcache: fix serialization bug in zv stats

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Date:	Fri, 30 Dec 2011 10:42:15 -0600
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Brian King <brking@...ux.vnet.ibm.com>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: [PATCH] staging: zcache: fix serialization bug in zv stats

In a multithreaded workload, the zv_curr_dist_counts
and zv_cumul_dist_counts statistics are being corrupted
because the increments and decrements in zv_create
and zv_free are not atomic.

This patch converts these statistics and their corresponding
increments/decrements/reads to atomic operations.

Based on v3.2-rc7

Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
---
 drivers/staging/zcache/zcache-main.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/zcache/zcache-main.c b/drivers/staging/zcache/zcache-main.c
index 56c1f9c..d39bb51 100644
--- a/drivers/staging/zcache/zcache-main.c
+++ b/drivers/staging/zcache/zcache-main.c
@@ -655,8 +655,8 @@ static unsigned int zv_max_zsize = (PAGE_SIZE / 8) * 7;
  */
 static unsigned int zv_max_mean_zsize = (PAGE_SIZE / 8) * 5;
 
-static unsigned long zv_curr_dist_counts[NCHUNKS];
-static unsigned long zv_cumul_dist_counts[NCHUNKS];
+static atomic_t zv_curr_dist_counts[NCHUNKS];
+static atomic_t zv_cumul_dist_counts[NCHUNKS];
 
 static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id,
 				struct tmem_oid *oid, uint32_t index,
@@ -675,8 +675,8 @@ static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id,
 			&page, &offset, ZCACHE_GFP_MASK);
 	if (unlikely(ret))
 		goto out;
-	zv_curr_dist_counts[chunks]++;
-	zv_cumul_dist_counts[chunks]++;
+	atomic_inc(&zv_curr_dist_counts[chunks]);
+	atomic_inc(&zv_cumul_dist_counts[chunks]);
 	zv = kmap_atomic(page, KM_USER0) + offset;
 	zv->index = index;
 	zv->oid = *oid;
@@ -698,7 +698,7 @@ static void zv_free(struct xv_pool *xvpool, struct zv_hdr *zv)
 
 	ASSERT_SENTINEL(zv, ZVH);
 	BUG_ON(chunks >= NCHUNKS);
-	zv_curr_dist_counts[chunks]--;
+	atomic_dec(&zv_curr_dist_counts[chunks]);
 	size -= sizeof(*zv);
 	BUG_ON(size == 0);
 	INVERT_SENTINEL(zv, ZVH);
@@ -738,7 +738,7 @@ static int zv_curr_dist_counts_show(char *buf)
 	char *p = buf;
 
 	for (i = 0; i < NCHUNKS; i++) {
-		n = zv_curr_dist_counts[i];
+		n = atomic_read(&zv_curr_dist_counts[i]);
 		p += sprintf(p, "%lu ", n);
 		chunks += n;
 		sum_total_chunks += i * n;
@@ -754,7 +754,7 @@ static int zv_cumul_dist_counts_show(char *buf)
 	char *p = buf;
 
 	for (i = 0; i < NCHUNKS; i++) {
-		n = zv_cumul_dist_counts[i];
+		n = atomic_read(&zv_cumul_dist_counts[i]);
 		p += sprintf(p, "%lu ", n);
 		chunks += n;
 		sum_total_chunks += i * n;
-- 
1.7.5.4

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