[PATCH] dm-multipath: fix stall on noflush suspend/resume
Allow noflush suspend/resume of device-mapper device only for the case
where the device size is unchanged.
Otherwise, dm-multipath devices can stall when resumed if noflush was used
when suspending them, all paths have failed and queue_if_no_path is set.
Explanation:
1. Something is doing fsync() on the block dev,
holding inode->i_sem
2. The fsync write is blocked by all-paths-down and queue_if_no_path
3. Someone requests to suspend the dm device with noflush.
Pending writes are left in queue.
4. In the middle of dm_resume(), __bind() tries to get
inode->i_sem to do __set_size() and waits forever.
'noflush suspend' is a new device-mapper feature introduced in
early 2.6.20. So I hope the fix being included before 2.6.20 is
released.
Example of reproducer:
1. Create a multipath device by dmsetup
2. Fail all paths during mkfs
3. Do dmsetup suspend --noflush and load new map with healthy paths
4. Do dmsetup resume
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Acked-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index fe7c56e..3668b17 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1116,7 +1116,8 @@
if (size != get_capacity(md->disk))
memset(&md->geometry, 0, sizeof(md->geometry));
- __set_size(md, size);
+ if (md->suspended_bdev)
+ __set_size(md, size);
if (size == 0)
return 0;
@@ -1264,6 +1265,11 @@
if (!dm_suspended(md))
goto out;
+ /* without bdev, the device size cannot be changed */
+ if (!md->suspended_bdev)
+ if (get_capacity(md->disk) != dm_table_get_size(table))
+ goto out;
+
__unbind(md);
r = __bind(md, table);
@@ -1341,11 +1347,14 @@
/* This does not get reverted if there's an error later. */
dm_table_presuspend_targets(map);
- md->suspended_bdev = bdget_disk(md->disk, 0);
- if (!md->suspended_bdev) {
- DMWARN("bdget failed in dm_suspend");
- r = -ENOMEM;
- goto flush_and_out;
+ /* bdget() can stall if the pending I/Os are not flushed */
+ if (!noflush) {
+ md->suspended_bdev = bdget_disk(md->disk, 0);
+ if (!md->suspended_bdev) {
+ DMWARN("bdget failed in dm_suspend");
+ r = -ENOMEM;
+ goto flush_and_out;
+ }
}
/*
@@ -1473,8 +1482,10 @@
unlock_fs(md);
- bdput(md->suspended_bdev);
- md->suspended_bdev = NULL;
+ if (md->suspended_bdev) {
+ bdput(md->suspended_bdev);
+ md->suspended_bdev = NULL;
+ }
clear_bit(DMF_SUSPENDED, &md->flags);