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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: 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>
Cc: stable@vger.kernel.org
master
Jan Kara 8 years ago
committed by Theodore Ts'o
parent
commit
34cf865d54
  1. 12
      fs/ext4/inode.c

12
fs/ext4/inode.c

@ -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;
}

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