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    Subject[PATCH 3.10 033/129] ext4: fix deadlock when writing in ENOSPC conditions
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/inode.c | 12 ------------
    1 file changed, 12 deletions(-)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -1263,7 +1263,6 @@ static int ext4_journalled_write_end(str
    */
    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;
    @@ -1275,7 +1274,6 @@ static int ext4_da_reserve_metadata(stru
    * 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
    @@ -1295,10 +1293,6 @@ 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;
    @@ -1312,7 +1306,6 @@ 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;
    @@ -1334,7 +1327,6 @@ static int ext4_da_reserve_space(struct
    * 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
    @@ -1354,10 +1346,6 @@ 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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