[PATCH 3.8 106/166] ext4: fix deadlock when writing in ENOSPC conditions

Kamal Mostafa
2014-01-15T21:52:00Z

From: Jan Kara <jack@suse.cz>

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@rs.jp.nec.com>
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
[ kamal: backport to 3.8 (no ext4_da_reserve_metadata) ]
Signed-off-by: Kamal Mostafa <kamal@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