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authorJianpeng Ma <majianpeng@gmail.com>2013-07-03 13:25:24 +0200
committerJens Axboe <axboe@kernel.dk>2013-07-03 13:25:24 +0200
commitd50235b7bc3ee0a0427984d763ea7534149531b4 (patch)
treeacf1916e7926c1a0dddbe08db11ca2426a3816cc /block/elevator.c
parenta6b3f7614ca690e49e934c291f707b0c19312194 (diff)
downloadblackbird-op-linux-d50235b7bc3ee0a0427984d763ea7534149531b4.tar.gz
blackbird-op-linux-d50235b7bc3ee0a0427984d763ea7534149531b4.zip
elevator: Fix a race in elevator switching
There's a race between elevator switching and normal io operation. Because the allocation of struct elevator_queue and struct elevator_data don't in a atomic operation.So there are have chance to use NULL ->elevator_data. For example: Thread A: Thread B blk_queu_bio elevator_switch spin_lock_irq(q->queue_block) elevator_alloc elv_merge elevator_init_fn Because call elevator_alloc, it can't hold queue_lock and the ->elevator_data is NULL.So at the same time, threadA call elv_merge and nedd some info of elevator_data.So the crash happened. Move the elevator_alloc into func elevator_init_fn, it make the operations in a atomic operation. Using the follow method can easy reproduce this bug 1:dd if=/dev/sdb of=/dev/null 2:while true;do echo noop > scheduler;echo deadline > scheduler;done The test method also use this method. Signed-off-by: Jianpeng Ma <majianpeng@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/elevator.c')
-rw-r--r--block/elevator.c25
1 files changed, 5 insertions, 20 deletions
diff --git a/block/elevator.c b/block/elevator.c
index eba5b04c29b1..668394d18588 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -150,7 +150,7 @@ void __init load_default_elevator_module(void)
static struct kobj_type elv_ktype;
-static struct elevator_queue *elevator_alloc(struct request_queue *q,
+struct elevator_queue *elevator_alloc(struct request_queue *q,
struct elevator_type *e)
{
struct elevator_queue *eq;
@@ -170,6 +170,7 @@ err:
elevator_put(e);
return NULL;
}
+EXPORT_SYMBOL(elevator_alloc);
static void elevator_release(struct kobject *kobj)
{
@@ -221,16 +222,7 @@ int elevator_init(struct request_queue *q, char *name)
}
}
- q->elevator = elevator_alloc(q, e);
- if (!q->elevator)
- return -ENOMEM;
-
- err = e->ops.elevator_init_fn(q);
- if (err) {
- kobject_put(&q->elevator->kobj);
- return err;
- }
-
+ err = e->ops.elevator_init_fn(q, e);
return 0;
}
EXPORT_SYMBOL(elevator_init);
@@ -935,16 +927,9 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
spin_unlock_irq(q->queue_lock);
/* allocate, init and register new elevator */
- err = -ENOMEM;
- q->elevator = elevator_alloc(q, new_e);
- if (!q->elevator)
- goto fail_init;
-
- err = new_e->ops.elevator_init_fn(q);
- if (err) {
- kobject_put(&q->elevator->kobj);
+ err = new_e->ops.elevator_init_fn(q, new_e);
+ if (err)
goto fail_init;
- }
if (registered) {
err = elv_register_queue(q);
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