From 7f3b5ef8184a929f56293d6c7a88f426c7b74558 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 21 Sep 2011 15:30:20 +1000 Subject: md: Avoid waking up a thread after it has been freed. commit 01f96c0a9922cd9919baf9d16febdf7016177a12 upstream. 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: "Moshe Melnikov" Signed-off-by: NeilBrown Signed-off-by: Greg Kroah-Hartman --- drivers/md/md.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) (limited to 'drivers/md/md.c') diff --git a/drivers/md/md.c b/drivers/md/md.c index 85540829d64c..bc8342812d06 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -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); @@ -690,7 +695,12 @@ 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) @@ -6186,11 +6196,18 @@ 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); @@ -7125,8 +7142,7 @@ 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...*/ -- cgit v1.2.3