[PATCH] device-mapper multipath: Avoid possible suspension deadlock

To avoid deadlock when suspending a multipath device after all its paths have
failed, stop queueing any I/O that is about to fail *before* calling
freeze_bdev instead of after.

Instead of setting a multipath 'suspended' flag which would have to be reset
if an error occurs during the process, save the previous queueing state and
leave userspace to restore if it wishes.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 5d40555b42ba..bb3ad79c14d7 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1055,14 +1055,17 @@ int dm_suspend(struct mapped_device *md)
         if (test_bit(DMF_BLOCK_IO, &md->flags))
                 goto out_read_unlock;
 
-        error = __lock_fs(md);
-        if (error)
-                goto out_read_unlock;
-
         map = dm_get_table(md);
         if (map)
+                /* This does not get reverted if there's an error later. */
                 dm_table_presuspend_targets(map);
 
+        error = __lock_fs(md);
+        if (error) {
+                dm_table_put(map);
+                goto out_read_unlock;
+        }
+
         up_read(&md->lock);
 
         /*
@@ -1121,7 +1124,6 @@ int dm_suspend(struct mapped_device *md)
         return 0;
 
 out_unfreeze:
-        /* FIXME Undo dm_table_presuspend_targets */
         __unlock_fs(md);
         clear_bit(DMF_BLOCK_IO, &md->flags);
 out_write_unlock: