Commit 01f96c0a authored by NeilBrown's avatar NeilBrown
Browse files

md: Avoid waking up a thread after it has been freed. 



Two related problems:

1/ some error paths call "md_unregister_thread(mddev->thread)"
   without subsequently clearing ->thread.  A subsequent call
   to mddev_unlock will try to wake the thread, and crash.

2/ Most calls to md_wakeup_thread are protected against the thread
   disappeared either by:
      - holding the ->mutex
      - having an active request, so something else must be keeping
        the array active.
   However mddev_unlock calls md_wakeup_thread after dropping the
   mutex and without any certainty of an active request, so the
   ->thread could theoretically disappear.
   So we need a spinlock to provide some protections.

So change md_unregister_thread to take a pointer to the thread
pointer, and ensure that it always does the required locking, and
clears the pointer properly.

Reported-by: default avatar"Moshe Melnikov" <moshe@zadarastorage.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
cc: stable@kernel.org
parent 27a7b260

drivers/md/md.c

+19 −3
Original line number Diff line number Diff line
@@ -61,6 +61,11 @@ 
static void autostart_arrays(int part);

#endif



/* pers_list is a list of registered personalities protected

 * by pers_lock.

 * pers_lock does extra service to protect accesses to

 * mddev->thread when the mutex cannot be held.

 */

static LIST_HEAD(pers_list);

static DEFINE_SPINLOCK(pers_lock);
@@ -739,7 +744,12 @@ static void mddev_unlock(mddev_t * mddev) 
	} else

		mutex_unlock(&mddev->reconfig_mutex);



	/* was we've dropped the mutex we need a spinlock to

	 * make sur the thread doesn't disappear

	 */

	spin_lock(&pers_lock);

	md_wakeup_thread(mddev->thread);

	spin_unlock(&pers_lock);

}



static mdk_rdev_t * find_rdev_nr(mddev_t *mddev, int nr)
@@ -6429,11 +6439,18 @@ mdk_thread_t *md_register_thread(void (*run) (mddev_t *), mddev_t *mddev, 
	return thread;

}



void md_unregister_thread(mdk_thread_t *thread)

void md_unregister_thread(mdk_thread_t **threadp)

{

	mdk_thread_t *thread = *threadp;

	if (!thread)

		return;

	dprintk("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));

	/* Locking ensures that mddev_unlock does not wake_up a

	 * non-existent thread

	 */

	spin_lock(&pers_lock);

	*threadp = NULL;

	spin_unlock(&pers_lock);



	kthread_stop(thread->tsk);

	kfree(thread);
@@ -7340,8 +7357,7 @@ static void reap_sync_thread(mddev_t *mddev) 
	mdk_rdev_t *rdev;



	/* resync has finished, collect result */

	md_unregister_thread(mddev->sync_thread);

	mddev->sync_thread = NULL;

	md_unregister_thread(&mddev->sync_thread);

	if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&

	    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {

		/* success...*/

drivers/md/md.h

+1 −1
Original line number Diff line number Diff line
@@ -560,7 +560,7 @@ extern int register_md_personality(struct mdk_personality *p); 
extern int unregister_md_personality(struct mdk_personality *p);

extern mdk_thread_t * md_register_thread(void (*run) (mddev_t *mddev),

				mddev_t *mddev, const char *name);

extern void md_unregister_thread(mdk_thread_t *thread);

extern void md_unregister_thread(mdk_thread_t **threadp);

extern void md_wakeup_thread(mdk_thread_t *thread);

extern void md_check_recovery(mddev_t *mddev);

extern void md_write_start(mddev_t *mddev, struct bio *bi);

drivers/md/multipath.c

+1 −2
Original line number Diff line number Diff line
@@ -514,8 +514,7 @@ static int multipath_stop (mddev_t *mddev) 
{

	multipath_conf_t *conf = mddev->private;



	md_unregister_thread(mddev->thread);

	mddev->thread = NULL;

	md_unregister_thread(&mddev->thread);

	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/

	mempool_destroy(conf->pool);

	kfree(conf->multipaths);

drivers/md/raid1.c

+1 −2
Original line number Diff line number Diff line
@@ -2562,8 +2562,7 @@ static int stop(mddev_t *mddev) 
	raise_barrier(conf);

	lower_barrier(conf);



	md_unregister_thread(mddev->thread);

	mddev->thread = NULL;

	md_unregister_thread(&mddev->thread);

	if (conf->r1bio_pool)

		mempool_destroy(conf->r1bio_pool);

	kfree(conf->mirrors);

drivers/md/raid10.c

+2 −3
Original line number Diff line number Diff line
@@ -2955,7 +2955,7 @@ static int run(mddev_t *mddev) 
	return 0;



out_free_conf:

	md_unregister_thread(mddev->thread);

	md_unregister_thread(&mddev->thread);

	if (conf->r10bio_pool)

		mempool_destroy(conf->r10bio_pool);

	safe_put_page(conf->tmppage);
@@ -2973,8 +2973,7 @@ static int stop(mddev_t *mddev) 
	raise_barrier(conf, 0);

	lower_barrier(conf);



	md_unregister_thread(mddev->thread);

	mddev->thread = NULL;

	md_unregister_thread(&mddev->thread);

	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/

	if (conf->r10bio_pool)

		mempool_destroy(conf->r10bio_pool);

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