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H A Dmempool.cdiff 0b1d647a02c5a1b67d45287eeb6cb3b2219c41c3 Thu Aug 31 23:27:47 CDT 2006 Pavel Mironchik <tibor0@gmail.com> [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: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>