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blk-throttle: Free up a group only after one rcu grace period

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Soon we will allow accessing a throtl_grp under rcu_read_lock(). Hence
start freeing up throtl_grp after one rcu grace period.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Vivek Goyal 2011-05-19 15:38:27 -04:00 committed by Jens Axboe
parent 5617cbef77
commit 4843c69d49
1 changed files with 21 additions and 1 deletions
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22
block/blk-throttle.c
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@ -78,6 +78,8 @@ struct throtl_grp {
/* Some throttle limits got updated for the group */ /* Some throttle limits got updated for the group */
int limits_changed; int limits_changed;
struct rcu_head rcu_head;
}; };
struct throtl_data struct throtl_data
@ -151,12 +153,30 @@ static inline struct throtl_grp *throtl_ref_get_tg(struct throtl_grp *tg)
return tg; return tg;
} }
static void throtl_free_tg(struct rcu_head *head)
{
struct throtl_grp *tg;
tg = container_of(head, struct throtl_grp, rcu_head);
kfree(tg);
}
static void throtl_put_tg(struct throtl_grp *tg) static void throtl_put_tg(struct throtl_grp *tg)
{ {
BUG_ON(atomic_read(&tg->ref) <= 0); BUG_ON(atomic_read(&tg->ref) <= 0);
if (!atomic_dec_and_test(&tg->ref)) if (!atomic_dec_and_test(&tg->ref))
return; return;
kfree(tg);
/*
* A group is freed in rcu manner. But having an rcu lock does not
* mean that one can access all the fields of blkg and assume these
* are valid. For example, don't try to follow throtl_data and
* request queue links.
*
* Having a reference to blkg under an rcu allows acess to only
* values local to groups like group stats and group rate limits
*/
call_rcu(&tg->rcu_head, throtl_free_tg);
} }
static void throtl_init_group(struct throtl_grp *tg) static void throtl_init_group(struct throtl_grp *tg)