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Subject[PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array.

Due to possible deadlock issues we need to use a schedule work to
kobject_del an 'rdev' object from a different thread.

A recent change means that kobject_add no longer gets a refernce, and
kobject_del doesn't put a reference. Consequently, we need to
explicitly hold a reference to ensure that the last reference isn't
dropped before the scheduled work get a chance to call kobject_del.

Also, rename delayed_delete to md_delayed_delete to that it is more
obvious in a stack trace which code is to blame.

Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
./drivers/md/md.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c 2008-01-14 12:23:53.000000000 +1100
+++ ./drivers/md/md.c 2008-01-14 12:24:17.000000000 +1100
@@ -1421,10 +1421,11 @@ static int bind_rdev_to_array(mdk_rdev_t
return err;
}

-static void delayed_delete(struct work_struct *ws)
+static void md_delayed_delete(struct work_struct *ws)
{
mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
kobject_del(&rdev->kobj);
+ kobject_put(&rdev->kobj);
}

static void unbind_rdev_from_array(mdk_rdev_t * rdev)
@@ -1443,7 +1444,8 @@ static void unbind_rdev_from_array(mdk_r
/* We need to delay this, otherwise we can deadlock when
* writing to 'remove' to "dev/state"
*/
- INIT_WORK(&rdev->del_work, delayed_delete);
+ INIT_WORK(&rdev->del_work, md_delayed_delete);
+ kobject_get(&rdev->kobj);
schedule_work(&rdev->del_work);
}

@@ -3688,7 +3690,7 @@ static int do_md_stop(mddev_t * mddev, i
sysfs_remove_link(&mddev->kobj, nm);
}

- /* make sure all delayed_delete calls have finished */
+ /* make sure all md_delayed_delete calls have finished */
flush_scheduled_work();

export_array(mddev);

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