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cfq-iosched: do not leak ioc_data across iosched switches 

When switching scheduler from cfq, cfq_exit_queue() does not clear
ioc->ioc_data, leaving a dangling pointer that can deceive the following
lookups when the iosched is switched back to cfq.  The pattern that can
trigger that is the following:

    - elevator switch from cfq to something else;
    - module unloading, with elv_unregister() that calls cfq_free_io_context()
      on ioc freeing the cic (via the .trim op);
    - module gets reloaded and the elevator switches back to cfq;
    - reallocation of a cic at the same address as before (with a valid key).

To fix it just assign NULL to ioc_data in __cfq_exit_single_io_context(),
that is called from the regular exit path and from the elevator switching
code.  The only path that frees a cic and is not covered is the error handling
one, but cic's freed in this way are never cached in ioc_data.

Signed-off-by: Fabio Checconi <fabio@gandalf.sssup.it>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Fabio Checconi 2008-04-10 08:28:01 +02:00 committed by Jens Axboe
parent 8191ecd1d1
commit 4faa3c8150
1 changed files with 6 additions and 3 deletions
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9
block/cfq-iosched.c
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@ -1214,6 +1214,8 @@ static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
struct cfq_io_context *cic)
{
struct io_context *ioc = cic->ioc;
list_del_init(&cic->queue_list);
/*
@ -1223,6 +1225,9 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
cic->dead_key = (unsigned long) cic->key;
cic->key = NULL;
if (ioc->ioc_data == cic)
rcu_assign_pointer(ioc->ioc_data, NULL);
if (cic->cfqq[ASYNC]) {
cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);
cic->cfqq[ASYNC] = NULL;
@ -1255,7 +1260,6 @@ static void cfq_exit_single_io_context(struct io_context *ioc,
*/
static void cfq_exit_io_context(struct io_context *ioc)
{
rcu_assign_pointer(ioc->ioc_data, NULL);
call_for_each_cic(ioc, cfq_exit_single_io_context);
}
@ -1478,8 +1482,7 @@ cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
spin_lock_irqsave(&ioc->lock, flags);
if (ioc->ioc_data == cic)
rcu_assign_pointer(ioc->ioc_data, NULL);
BUG_ON(ioc->ioc_data == cic);
radix_tree_delete(&ioc->radix_root, (unsigned long) cfqd);
hlist_del_rcu(&cic->cic_list);