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kernel-2.6.18-238.el5.src.rpm

From: Milan Broz <mbroz@redhat.com>
Subject: [RHEL 5.1 PATCH] dm: stalls on resume if noflush is used
Date: Tue, 10 Apr 2007 16:58:04 +0200
Bugzilla: 221330
Message-Id: <461BA5FC.5060707@redhat.com>
Changelog: [dm] stalls on resume if noflush is used


RHEL5.1 device mapper: stalls on resume if noflush is used

Resolves: rhbz#221330, it#110302

Patch in RHEL4.5 and upstream in 2.6.20.

Multipath devices can stall when resumed if noflush was used when
suspending them, all paths have failed and queue_if_no_path is set.

Mirroring and cluster mirroring is affected too.

Fix tested with both multipath and mirror cases.


Explanation:
 1 Something did fsync() on the block dev
   holding inode->i_sem and possibly I_LOCK is set
 2 The fsync write is blocked by all-paths-down and queue_if_no_path
 3 dm_suspend() tries to bdget() and waits forever on the inode
   being unlocked.
   Or, in the middle of dm_resume(), __bind() tries to get
   inode->i_sem to do __set_size() and waits forever

What the patch does is:
  - Skip bdget_disk() in case of noflush suspending
  - At the table swapping, if bdget_disk() has not been done,
    check if the table size is being changed.
    If it's being changed, quit the swapping.
  - Check before __set_size() whether bdget_disk() has been done.
    (for the case where table size isn't changed during noflush)


Index: linux-2.6.18/drivers/md/dm.c
===================================================================
--- linux-2.6.18.orig/drivers/md/dm.c	2007-04-10 11:40:51.000000000 +0200
+++ linux-2.6.18/drivers/md/dm.c	2007-04-10 16:52:51.000000000 +0200
@@ -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;
 
@@ -1264,6 +1265,11 @@ 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);
 
@@ -1341,11 +1347,14 @@ 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;
+		}
 	}
 
 	/*
@@ -1471,8 +1480,10 @@ 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);