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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: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -238,8 +238,13 @@ repeat_alloc:
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init_wait(&wait);
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prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
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smp_mb();
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if (!pool->curr_nr)
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io_schedule();
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if (!pool->curr_nr) {
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/*
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* FIXME: this should be io_schedule(). The timeout is there
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* as a workaround for some DM problems in 2.6.18.
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*/
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io_schedule_timeout(5*HZ);
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}
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finish_wait(&pool->wait, &wait);
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goto repeat_alloc;
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