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

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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" <moshe@zadarastorage.com>
Signed-off-by: NeilBrown <neilb@suse.de>
cc: stable@kernel.org
This commit is contained in:
NeilBrown 2011-09-21 15:30:20 +10:00
parent 27a7b260f7
commit 01f96c0a99
6 changed files with 26 additions and 15 deletions
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3
drivers/md/raid1.c
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@ -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);