lkml.org 
[lkml]   [2007]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 2.6.20-rc5] 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.

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

---
'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


drivers/md/dm.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
Index: linux-2.6.19/drivers/md/dm.c
===================================================================
--- linux-2.6.19.orig/drivers/md/dm.c 2006-12-12 22:02:29.000000000 +0000
+++ linux-2.6.19/drivers/md/dm.c 2007-01-05 15:15:53.000000000 +0000
@@ -1116,7 +1116,8 @@ static int __bind(struct mapped_device *
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;

@@ -1265,6 +1266,11 @@ int dm_swap_table(struct mapped_device *
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);

@@ -1342,11 +1348,14 @@ int dm_suspend(struct mapped_device *md,
/* 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;
+ }
}

/*
@@ -1474,8 +1483,10 @@ int dm_resume(struct mapped_device *md)

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);
\
 
 \ /
  Last update: 2007-01-20 02:43    [from the cache]
©2003-2011 Jasper Spaans