linux-kernel - Re: [dm-devel] [BUG] kernel 2.6.32.x hangs during boot process

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Message-ID: <4B612F89.7020503@ce.jp.nec.com>
Date:	Thu, 28 Jan 2010 15:32:41 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	François Figarola 
	<francois.figarola@...onsult.fr>, hch@...radead.org
CC:	device-mapper development <dm-devel@...hat.com>,
	linux-kernel@...r.kernel.org, Neil Brown <neilb@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-raid@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [dm-devel] [BUG] kernel 2.6.32.x hangs during boot process

>> On Sat, 16 Jan 2010 10:58:30 +0100
>> Fran__ois Figarola  <francois.figarola@...onsult.fr> wrote:
>>> Since I've tried to boot 2.6.32.x kernel, my system hangs during the
>>> boot process, and I think it could be related to the problem reported
>>> earlier by Megastorage (http://lkml.org/lkml/2010/1/10/92).
>>>
>>> The hardware is a Dell PowerEdge 2950 which runs fine with the
>>> 2.6.31.x kernel series (actually running with the latest 2.6.31.11),
>>> and the system is debian etch.
>>>
>>> Here is the trace of the bug I've got (using netconsole) with a
>>> 2.6.32.3 kernel :
>>>
>>> BUG: Dentry ffff880667690000{i=41a46,n=sleep} still in use (8)
>>> [unmount of ext3 dm-4]
>>> ------------[ cut here ]------------
>>> kernel BUG at fs/dcache.c:670!

I can reproduce this when suspend/resume read-only mounted dm device.

When MS_RDONLY, both freeze_bdev and thaw_bdev call deactivate_locked_super,
which seems wrong. The change was introduced with the commit below:

  commit 4504230a71566785a05d3e6b53fa1ee071b864eb
  Author: Christoph Hellwig <hch@....de>
  Date:   Mon Aug 3 23:28:35 2009 +0200

  freeze_bdev: grab active reference to frozen superblocks

With the attached patch, both remount-ro and remount-rw are
rejected as EBUSY on freezed device as expected.

Christoph, do you think this is the right fix?

-- 
Jun'ichi Nomura, NEC Corporation


If MS_RDONLY, freeze_bdev should just up_write(s_umount) instead of
deactivate_locked_super().
Also, keep sb->s_frozen consistent so that remount can check the frozen state.

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

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 73d6a73..600261f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -246,7 +246,9 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 	if (!sb)
 		goto out;
 	if (sb->s_flags & MS_RDONLY) {
-		deactivate_locked_super(sb);
+		sb->s_frozen = SB_FREEZE_TRANS;
+		smp_wmb();
+		up_write(&sb->s_umount);
 		mutex_unlock(&bdev->bd_fsfreeze_mutex);
 		return sb;
 	}
@@ -307,7 +309,7 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 	BUG_ON(sb->s_bdev != bdev);
 	down_write(&sb->s_umount);
 	if (sb->s_flags & MS_RDONLY)
-		goto out_deactivate;
+		goto out_unfrozen;
 
 	if (sb->s_op->unfreeze_fs) {
 		error = sb->s_op->unfreeze_fs(sb);
@@ -321,11 +323,11 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 		}
 	}
 
+out_unfrozen:
 	sb->s_frozen = SB_UNFROZEN;
 	smp_wmb();
 	wake_up(&sb->s_wait_unfrozen);
 
-out_deactivate:
 	if (sb)
 		deactivate_locked_super(sb);
 out_unlock:
--
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