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cfq-iosched: fix RCU race in the cfq io_context destructor handling

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put_io_context() drops the RCU read lock before calling into cfq_dtor(),
however we need to hold off freeing there before grabbing and
dereferencing the first object on the list.

So extend the rcu_read_lock() scope to cover the calling of cfq_dtor(),
and optimize cfq_free_io_context() to use a new variant for
call_for_each_cic() that assumes the RCU read lock is already held.

Hit in the wild by Alexey Dobriyan <adobriyan@gmail.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-05-07 09:17:12 +02:00
parent aa94b5371f
commit 07416d29bc
2 changed files with 14 additions and 7 deletions
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2
block/blk-ioc.c
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@ -41,8 +41,8 @@ int put_io_context(struct io_context *ioc)
rcu_read_lock();
if (ioc->aic && ioc->aic->dtor)
ioc->aic->dtor(ioc->aic);
rcu_read_unlock();
cfq_dtor(ioc);
rcu_read_unlock();
kmem_cache_free(iocontext_cachep, ioc);
return 1;

19
block/cfq-iosched.c
View File

@ -1142,6 +1142,17 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
kmem_cache_free(cfq_pool, cfqq);
}
static void
__call_for_each_cic(struct io_context *ioc,
void (*func)(struct io_context *, struct cfq_io_context *))
{
struct cfq_io_context *cic;
struct hlist_node *n;
hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
func(ioc, cic);
}
/*
* Call func for each cic attached to this ioc.
*/
@ -1149,12 +1160,8 @@ static void
call_for_each_cic(struct io_context *ioc,
void (*func)(struct io_context *, struct cfq_io_context *))
{
struct cfq_io_context *cic;
struct hlist_node *n;
rcu_read_lock();
hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
func(ioc, cic);
__call_for_each_cic(ioc, func);
rcu_read_unlock();
}
@ -1198,7 +1205,7 @@ static void cfq_free_io_context(struct io_context *ioc)
* should be ok to iterate over the known list, we will see all cic's
* since no new ones are added.
*/
call_for_each_cic(ioc, cic_free_func);
__call_for_each_cic(ioc, cic_free_func);
}
static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)