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Commit 5f45c695 authored by Jens Axboe's avatar Jens Axboe
Browse files

cfq-iosched: read_lock() does not always imply rcu_read_lock() 



For some configurations of CONFIG_PREEMPT that is not true. So
get rid of __call_for_each_cic() and always uses the explicitly
rcu_read_lock() protected call_for_each_cic() instead.

This fixes a potential bug related to IO scheduler removal or
online switching.

Thanks to Paul McKenney for clarifying this.

Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent bd900d45

block/cfq-iosched.c

+6 −14
Original line number Diff line number Diff line
@@ -2582,28 +2582,20 @@ static void cfq_put_queue(struct cfq_queue *cfqq) 
}



/*

 * Must always be called with the rcu_read_lock() held

 * 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();

}
@@ -2664,7 +2656,7 @@ 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_put_cooperator(struct cfq_queue *cfqq)