[3.5.y.z extended stable] Patch "ext4: fix deadlock when writing in ENOSPC conditions" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ext4: fix deadlock when writing in ENOSPC conditions

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 3eab8e353024299201e8956f10e659213f3cd375 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.cz>
Date: Wed, 18 Dec 2013 00:44:44 -0500
Subject: ext4: fix deadlock when writing in ENOSPC conditions

commit 34cf865d54813aab3497838132fb1bbd293f4054 upstream.

Akira-san has been reporting rare deadlocks of his machine when running
xfstests test 269 on ext4 filesystem. The problem turned out to be in
ext4_da_reserve_metadata() and ext4_da_reserve_space() which called
ext4_should_retry_alloc() while holding i_data_sem. Since
ext4_should_retry_alloc() can force a transaction commit, this is a
lock ordering violation and leads to deadlocks.

Fix the problem by just removing the retry loops. These functions should
just report ENOSPC to the caller (e.g. ext4_da_write_begin()) and that
function must take care of retrying after dropping all necessary locks.

Reported-and-tested-by: Akira Fujita <a-fujita at rs.jp.nec.com>
Reviewed-by: Zheng Liu <wenqing.lz at taobao.com>
Signed-off-by: Jan Kara <jack at suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
[ kamal: backport to 3.8 (no ext4_da_reserve_metadata) ]
Cc: Kamal Mostafa <kamal at canonical.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/ext4/inode.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 8aacdda..efecfb7 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1175,7 +1175,6 @@ static int ext4_journalled_write_end(struct file *file,
  */
 static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
 {
-	int retries = 0;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	unsigned int md_needed;
@@ -1197,7 +1196,6 @@ static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
 	 * in order to allocate nrblocks
 	 * worse case is one extent per block
 	 */
-repeat:
 	spin_lock(&ei->i_block_reservation_lock);
 	/*
 	 * ext4_calc_metadata_amount() has side effects, which we have
@@ -1217,10 +1215,6 @@ repeat:
 		ei->i_da_metadata_calc_len = save_len;
 		ei->i_da_metadata_calc_last_lblock = save_last_lblock;
 		spin_unlock(&ei->i_block_reservation_lock);
-		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
-			yield();
-			goto repeat;
-		}
 		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
 		return -ENOSPC;
 	}
--
1.8.3.2