path: root/block/as-iosched.c
diff options
authorJens Axboe <axboe@suse.de>2006-06-08 08:49:06 +0200
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-08 15:14:23 -0700
commitbc1c116974a5c3f498112a6f175d3e4a8cd5bdbc (patch)
tree69ea68db91fb871cd24a0a5c5045abbe9c77bd3a /block/as-iosched.c
parent26e780e8ef1cc3ef581a07aafe2346bb5a07b4f9 (diff)
[PATCH] elevator switching race
There's a race between shutting down one io scheduler and firing up the next, in which a new io could enter and cause the io scheduler to be invoked with bad or NULL data. To fix this, we need to maintain the queue lock for a bit longer. Unfortunately we cannot do that, since the elevator init requires to be run without the lock held. This isn't easily fixable, without also changing the mempool API. So split the initialization into two parts, and alloc-init operation and an attach operation. Then we can preallocate the io scheduler and related structures, and run the attach inside the lock after we detach the old one. This patch has survived 30 minutes of 1 second io scheduler switching with a very busy io load. Signed-off-by: Jens Axboe <axboe@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'block/as-iosched.c')
1 files changed, 6 insertions, 7 deletions
diff --git a/block/as-iosched.c b/block/as-iosched.c
index e25a5d79ab2..a7caf35ca0c 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -1648,17 +1648,17 @@ static void as_exit_queue(elevator_t *e)
* initialize elevator private data (as_data), and alloc a arq for
* each request on the free lists
-static int as_init_queue(request_queue_t *q, elevator_t *e)
+static void *as_init_queue(request_queue_t *q, elevator_t *e)
struct as_data *ad;
int i;
if (!arq_pool)
- return -ENOMEM;
+ return NULL;
ad = kmalloc_node(sizeof(*ad), GFP_KERNEL, q->node);
if (!ad)
- return -ENOMEM;
+ return NULL;
memset(ad, 0, sizeof(*ad));
ad->q = q; /* Identify what queue the data belongs to */
@@ -1667,7 +1667,7 @@ static int as_init_queue(request_queue_t *q, elevator_t *e)
GFP_KERNEL, q->node);
if (!ad->hash) {
- return -ENOMEM;
+ return NULL;
ad->arq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
@@ -1675,7 +1675,7 @@ static int as_init_queue(request_queue_t *q, elevator_t *e)
if (!ad->arq_pool) {
- return -ENOMEM;
+ return NULL;
/* anticipatory scheduling helpers */
@@ -1696,14 +1696,13 @@ static int as_init_queue(request_queue_t *q, elevator_t *e)
ad->antic_expire = default_antic_expire;
ad->batch_expire[REQ_SYNC] = default_read_batch_expire;
ad->batch_expire[REQ_ASYNC] = default_write_batch_expire;
- e->elevator_data = ad;
ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC];
ad->write_batch_count = ad->batch_expire[REQ_ASYNC] / 10;
if (ad->write_batch_count < 2)
ad->write_batch_count = 2;
- return 0;
+ return ad;