Commit 34cf865d authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
Browse files

ext4: fix deadlock when writing in ENOSPC conditions 



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: default avatarAkira Fujita <a-fujita@rs.jp.nec.com>
Reviewed-by: default avatarZheng Liu <wenqing.lz@taobao.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent a67c848a

fs/ext4/inode.c

+0 −12
Original line number Diff line number Diff line
@@ -1206,7 +1206,6 @@ static int ext4_journalled_write_end(struct file *file, 
 */

static int ext4_da_reserve_metadata(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;
@@ -1218,7 +1217,6 @@ static int ext4_da_reserve_metadata(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
@@ -1238,10 +1236,6 @@ 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)) {

			cond_resched();

			goto repeat;

		}

		return -ENOSPC;

	}

	ei->i_reserved_meta_blocks += md_needed;
@@ -1255,7 +1249,6 @@ repeat: 
 */

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;
@@ -1277,7 +1270,6 @@ 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
@@ -1297,10 +1289,6 @@ 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)) {

			cond_resched();

			goto repeat;

		}

		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));

		return -ENOSPC;

	}

CRA Git | Maintained and supported by SUSTech CRA and CCSE