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

[Kamal Mostafa]

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-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.16.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From e2aae703c185be4d1c2a0b3e157c7e6241d8781d 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) ]
Signed-off-by: Kamal Mostafa <kamal 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 fe1fada..46c10b5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1182,7 +1182,6 @@ 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;
@@ -1204,7 +1203,6 @@ 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
@@ -1224,10 +1222,6 @@ 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