staging: zcache: fix serialization bug in zv stats
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Message ID 1325263335-16254-1-git-send-email-sjenning@linux.vnet.ibm.com
State New, archived
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Series
  • staging: zcache: fix serialization bug in zv stats
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Commit Message

Seth Jennings Dec. 30, 2011, 4:42 p.m. UTC
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@linux.vnet.ibm.com>
---
 drivers/staging/zcache/zcache-main.c |   14 +++++++-------
 1 files changed, 7 insertions(+), 7 deletions(-)

Comments

Konrad Rzeszutek Wilk Jan. 3, 2012, 9:38 p.m. UTC | #1
On Fri, Dec 30, 2011 at 11:35:45AM -0600, Seth Jennings wrote:
> On 12/30/2011 11:02 AM, Dan Magenheimer wrote:
> >> From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com]
> >> Sent: Friday, December 30, 2011 9:42 AM
> >> To: Greg Kroah-Hartman
> >> Cc: Seth Jennings; Dan Magenheimer; Brian King; devel@driverdev.osuosl.org; linux-
> >> kernel@vger.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@linux.vnet.ibm.com>
> > 
> > I'm inclined to nack this change, at least unless inside an #ifdef DEBUG,
> 
> I guess I didn't respond to this suggestion.  We could put #ifdef DEBUG
> around the updates in zv_create and zv_free and around the two sysfs
> *_show functions.  Kinda messy though.  I guess it might not matter
> if we'll be re-evaluating this whole thing soon.

Perhaps also add in the TODO file that we want to move the stats collection
out of the code and only be enabled if CONFIG_DEBUGFS is set? (Which granted means
we need to implement the stats output in debugfs instead of sysfs).
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Seth Jennings Feb. 6, 2012, 9:18 p.m. UTC | #2
Hey Greg,

Just wanted to bump this fix again.  It's small and already Acked by
Dan Magenheimer.  It can go in an -rc release.

https://lkml.org/lkml/2011/12/30/48

Congrats on becoming a Linux Foundation Fellow!

--
Seth

On 12/30/2011 10:42 AM, Seth Jennings wrote:
> 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@linux.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;

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Patch
diff mbox series

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;