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Commit 07416d29 authored by Jens Axboe's avatar Jens Axboe
Browse files

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



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: default avatarJens Axboe <jens.axboe@oracle.com>
parent aa94b537

block/blk-ioc.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

block/cfq-iosched.c

+13 −6
Original line number Diff line number Diff line
@@ -1142,19 +1142,26 @@ static void cfq_put_queue(struct cfq_queue *cfqq) 
	kmem_cache_free(cfq_pool, cfqq);

}



/*

 * Call func for each cic attached to this ioc.

 */

static void

call_for_each_cic(struct io_context *ioc,

__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 func for each cic attached to this ioc.

 */

static void

call_for_each_cic(struct io_context *ioc,

		  void (*func)(struct io_context *, struct cfq_io_context *))

{

	rcu_read_lock();

	__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)