linux-kernel - [34-longterm 028/260] ext4: fix freeze deadlock under IO

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Date:	Sun,  2 Jan 2011 02:15:24 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Eric Sandeen <sandeen@...deen.net>,
	Eric Sandeen <sandeen@...hat.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 028/260] ext4: fix freeze deadlock under IO

From: Eric Sandeen <sandeen@...deen.net>

commit 437f88cc031ffe7f37f3e705367f4fe1f4be8b0f upstream.
[The 6b0310fb below references the mainline version of what
has also been cherry picked into this 34-stable branch]

Commit 6b0310fbf087ad6 caused a regression resulting in deadlocks
when freezing a filesystem which had active IO; the vfs_check_frozen
level (SB_FREEZE_WRITE) did not let the freeze-related IO syncing
through.  Duh.

Changing the test to FREEZE_TRANS should let the normal freeze
syncing get through the fs, but still block any transactions from
starting once the fs is completely frozen.

I tested this by running fsstress in the background while periodically
snapshotting the fs and running fsck on the result.  I ran into
occasional deadlocks, but different ones.  I think this is a
fine fix for the problem at hand, and the other deadlocky things
will need more investigation.

Reported-by: Phillip Susi <psusi@....rr.com>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 fs/ext4/super.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2aa9314..cd35e34 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -241,7 +241,7 @@ handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
 	if (sb->s_flags & MS_RDONLY)
 		return ERR_PTR(-EROFS);

-	vfs_check_frozen(sb, SB_FREEZE_WRITE);
+	vfs_check_frozen(sb, SB_FREEZE_TRANS);
 	/* Special case here: if the journal has aborted behind our
 	 * backs (eg. EIO in the commit thread), then we still need to
 	 * take the FS itself readonly cleanly. */
@@ -3485,7 +3485,7 @@ int ext4_force_commit(struct super_block *sb)

 	journal = EXT4_SB(sb)->s_journal;
 	if (journal) {
-		vfs_check_frozen(sb, SB_FREEZE_WRITE);
+		vfs_check_frozen(sb, SB_FREEZE_TRANS);
 		ret = ext4_journal_force_commit(journal);
 	}

-- 
1.7.3.3

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