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authorChandra Seetharaman <sekharan@us.ibm.com>2008-11-13 23:39:14 +0000
committerAlasdair G Kergon <agk@redhat.com>2008-11-13 23:39:14 +0000
commit8a57dfc6f943c92b861c9a19b0c86ddcb2aba768 (patch)
tree18090d42e647cda854c93aa304cf03fbad44f6c0 /drivers
parentd221d2e77696e70e94b13989ea15db2ba5b34f8e (diff)
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>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/dm.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index dc25d8a07bc..c99e4728ff4 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -937,16 +937,24 @@ static void dm_unplug_all(struct request_queue *q)
static int dm_any_congested(void *congested_data, int bdi_bits)
{
- int r;
- struct mapped_device *md = (struct mapped_device *) congested_data;
- struct dm_table *map = dm_get_table(md);
+ int r = bdi_bits;
+ struct mapped_device *md = congested_data;
+ struct dm_table *map;
- if (!map || test_bit(DMF_BLOCK_IO, &md->flags))
- r = bdi_bits;
- else
- r = dm_table_any_congested(map, bdi_bits);
+ atomic_inc(&md->pending);
+
+ if (!test_bit(DMF_BLOCK_IO, &md->flags)) {
+ map = dm_get_table(md);
+ if (map) {
+ r = dm_table_any_congested(map, bdi_bits);
+ dm_table_put(map);
+ }
+ }
+
+ if (!atomic_dec_return(&md->pending))
+ /* nudge anyone waiting on suspend queue */
+ wake_up(&md->wait);
- dm_table_put(map);
return r;
}