staging: zcache: fix serialization bug in zv stats
Seth Jennings [Fri, 30 Dec 2011 16:42:15 +0000 (10:42 -0600)]
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.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zcache/zcache-main.c

index ce07087..ef7c52b 100644 (file)
@@ -654,8 +654,8 @@ 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,
@@ -674,8 +674,8 @@ 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;
@@ -697,7 +697,7 @@ 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);
@@ -737,7 +737,7 @@ 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;
@@ -753,7 +753,7 @@ 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;