From: Chandra Seetharaman <sekharan@us.ibm.com>
Date: Thu, 13 Nov 2008 23:39:14 +0000 (+0000)
Subject: dm: avoid destroying table in dm_any_congested
X-Git-Tag: v2.6.28-rc5~17^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8a57dfc6f943c92b861c9a19b0c86ddcb2aba768;p=pandora-kernel.git

dm: avoid destroying table in dm_any_congested

dm_any_congested() just checks for the DMF_BLOCK_IO and has no
code to make sure that suspend waits for dm_any_congested() to
complete.  This patch adds such a check.

Without it, a race can occur with dm_table_put() attempting to
destroying the table in the wrong thread, the one running
dm_any_congested() which is meant to be quick and return
immediately.

Two examples of problems:
1. Sleeping functions called from congested code, the caller
   of which holds a spin lock.
2. An ABBA deadlock between pdflush and multipathd. The two locks
   in contention are inode lock and kernel lock.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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