cfq-iosched: fix alias + front merge bug

There's a really rare and obscure bug in CFQ, that causes a crash in
cfq_dispatch_insert() due to rq == NULL. One example of that is seen
here:

http://lkml.org/lkml/2007/4/15/41

Neil correctly diagnosed the situation for how this can happen, read
that analysis here:

http://lkml.org/lkml/2007/4/25/57

This looks like it requires md to trigger, even though it should
potentially be possible to due with O_DIRECT (at least if you edit the
kernel and doctor some of the unplug calls).

The fix is to move the ->next_rq update to when we add a request to the
rbtree. Then we remove the possibility for a request to exist in the
rbtree code, but not have ->next_rq correctly updated.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

0 files changed, 0 insertions, 0 deletions