tree 18090d42e647cda854c93aa304cf03fbad44f6c0
parent d221d2e77696e70e94b13989ea15db2ba5b34f8e
author Chandra Seetharaman <sekharan@us.ibm.com> 1226619554 +0000
committer Alasdair G Kergon <agk@redhat.com> 1226619554 +0000

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>