linux-kernel - [ 083/117] wake up s_wait_unfrozen when ->freeze

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Message-Id: <20120528031214.326681665@decadent.org.uk>
Date:	Mon, 28 May 2012 04:13:25 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Kazuya Mio <k-mio@...jp.nec.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: [ 083/117] wake up s_wait_unfrozen when ->freeze_fs fails

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kazuya Mio <k-mio@...jp.nec.com>

commit e1616300a20c80396109c1cf013ba9a36055a3da upstream.

dd slept infinitely when fsfeeze failed because of EIO.
To fix this problem, if ->freeze_fs fails, freeze_super() wakes up
the tasks waiting for the filesystem to become unfrozen.

When s_frozen isn't SB_UNFROZEN in __generic_file_aio_write(),
the function sleeps until FITHAW ioctl wakes up s_wait_unfrozen.

However, if ->freeze_fs fails, s_frozen is set to SB_UNFROZEN and then
freeze_super() returns an error number. In this case, FITHAW ioctl returns
EINVAL because s_frozen is already SB_UNFROZEN. There is no way to wake up
s_wait_unfrozen, so __generic_file_aio_write() sleeps infinitely.

Signed-off-by: Kazuya Mio <k-mio@...jp.nec.com>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/super.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index de41e1e..6015c02 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1186,6 +1186,8 @@ int freeze_super(struct super_block *sb)
 			printk(KERN_ERR
 				"VFS:Filesystem freeze failed\n");
 			sb->s_frozen = SB_UNFROZEN;
+			smp_wmb();
+			wake_up(&sb->s_wait_unfrozen);
 			deactivate_locked_super(sb);
 			return ret;
 		}

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