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

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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: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Jens Axboe 2011-04-19 09:10:35 +02:00
parent bd900d4580
commit 5f45c69589
1 changed files with 8 additions and 16 deletions
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24
block/cfq-iosched.c
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@ -2581,20 +2581,6 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
cfq_put_cfqg(cfqg);
}
/*
* Must always be called with the rcu_read_lock() held
*/
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.
*/
@ -2602,8 +2588,14 @@ 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();
__call_for_each_cic(ioc, func);
hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
func(ioc, cic);
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)