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[PATCH] fix try_module_get race in elevator_find

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This patch removes try_module_get race in elevator_find.
try_module_get should always be called with the spinlock protecting
what the module init/cleanup routines register/unregister to held. In
the case of elevators, we should be holding elv_list to avoid it going
away between spin_unlock_irq and try_module_get.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
This commit is contained in:
Tejun Heo 2005-10-20 10:56:41 +02:00 committed by Jens Axboe
parent b2982649ce
commit 2824bc9328
1 changed files with 14 additions and 10 deletions
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24
drivers/block/elevator.c
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@ -97,7 +97,6 @@ static struct elevator_type *elevator_find(const char *name)
struct elevator_type *e = NULL;
struct list_head *entry;
spin_lock_irq(&elv_list_lock);
list_for_each(entry, &elv_list) {
struct elevator_type *__e;
@ -108,7 +107,6 @@ static struct elevator_type *elevator_find(const char *name)
break;
}
}
spin_unlock_irq(&elv_list_lock);
return e;
}
@ -120,12 +118,15 @@ static void elevator_put(struct elevator_type *e)
static struct elevator_type *elevator_get(const char *name)
{
struct elevator_type *e = elevator_find(name);
struct elevator_type *e;
if (!e)
return NULL;
if (!try_module_get(e->elevator_owner))
return NULL;
spin_lock_irq(&elv_list_lock);
e = elevator_find(name);
if (e && !try_module_get(e->elevator_owner))
e = NULL;
spin_unlock_irq(&elv_list_lock);
return e;
}
@ -153,11 +154,15 @@ static char chosen_elevator[16];
static void elevator_setup_default(void)
{
struct elevator_type *e;
/*
* check if default is set and exists
*/
if (chosen_elevator[0] && elevator_find(chosen_elevator))
if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
elevator_put(e);
return;
}
#if defined(CONFIG_IOSCHED_AS)
strcpy(chosen_elevator, "anticipatory");
@ -555,10 +560,9 @@ void elv_unregister_queue(struct request_queue *q)
int elv_register(struct elevator_type *e)
{
spin_lock_irq(&elv_list_lock);
if (elevator_find(e->elevator_name))
BUG();
spin_lock_irq(&elv_list_lock);
list_add_tail(&e->list, &elv_list);
spin_unlock_irq(&elv_list_lock);