Commit 0b1d647a authored by Pavel Mironchik's avatar Pavel Mironchik Committed by Linus Torvalds
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[PATCH] dm: work around mempool_alloc, bio_alloc_bioset deadlocks

This patch works around a complex dm-related deadlock/livelock down in the
mempool allocator.

Alasdair said:

  Several dm targets suffer from this.

  Mempools are not yet used correctly everywhere in device-mapper: they can
  get shared when devices are stacked, and some targets share them across
  multiple instances.  I made fixing this one of the prerequisites for this
  patch:

    md-dm-reduce-stack-usage-with-stacked-block-devices.patch

  which in some cases makes people more likely to hit the problem.

  There's been some progress on this recently with (unfinished) dm-crypt
  patches at:

    http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/


      (dm-crypt-move-io-to-workqueue.patch plus dependencies)

and:

  I've no problems with a temporary workaround like that, but Milan Broz (a
  new Redhat developer in the Czech Republic) has started reviewing all the
  mempool usage in device-mapper so I'm expecting we'll soon have a proper fix
  for this associated problems.  [He's back from holiday at the start of next
  week.]

For now, this sad-but-safe little patch will allow the machine to recover.

[akpm@osdl.org: rewrote changelog]
Cc: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1e5f5e5c
......@@ -238,8 +238,13 @@ repeat_alloc:
init_wait(&wait);
prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
smp_mb();
if (!pool->curr_nr)
io_schedule();
if (!pool->curr_nr) {
/*
* FIXME: this should be io_schedule(). The timeout is there
* as a workaround for some DM problems in 2.6.18.
*/
io_schedule_timeout(5*HZ);
}
finish_wait(&pool->wait, &wait);
goto repeat_alloc;
......
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