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    Subject[patch 089/114] jbd2: Fix return value of jbd2_journal_start_commit()

    2.6.28-stable review patch. If anyone has any objections, please let us know.

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

    From: Jan Kara <jack@suse.cz>

    (cherry picked from commit c88ccea3143975294f5a52097546bcbb75975f52)

    The function jbd2_journal_start_commit() returns 1 if either a
    transaction is committing or the function has queued a transaction
    commit. But it returns 0 if we raced with somebody queueing the
    transaction commit as well. This resulted in ext4_sync_fs() not
    functioning correctly (description from Arthur Jones):

    In the case of a data=ordered umount with pending long symlinks
    which are delayed due to a long list of other I/O on the backing
    block device, this causes the buffer associated with the long
    symlinks to not be moved to the inode dirty list in the second
    phase of fsync_super. Then, before they can be dirtied again,
    kjournald exits, seeing the UMOUNT flag and the dirty pages are
    never written to the backing block device, causing long symlink
    corruption and exposing new or previously freed block data to
    userspace.

    This can be reproduced with a script created by Eric Sandeen
    <sandeen@redhat.com>:

    #!/bin/bash

    umount /mnt/test2
    mount /dev/sdb4 /mnt/test2
    rm -f /mnt/test2/*
    dd if=/dev/zero of=/mnt/test2/bigfile bs=1M count=512
    touch /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename
    ln -s /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename
    /mnt/test2/link
    umount /mnt/test2
    mount /dev/sdb4 /mnt/test2
    ls /mnt/test2/

    This patch fixes jbd2_journal_start_commit() to always return 1 when
    there's a transaction committing or queued for commit.

    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    CC: Eric Sandeen <sandeen@redhat.com>
    CC: linux-ext4@vger.kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/jbd2/journal.c | 17 +++++++++++------
    1 file changed, 11 insertions(+), 6 deletions(-)

    --- a/fs/jbd2/journal.c
    +++ b/fs/jbd2/journal.c
    @@ -430,7 +430,7 @@ int __jbd2_log_space_left(journal_t *jou
    }

    /*
    - * Called under j_state_lock. Returns true if a transaction was started.
    + * Called under j_state_lock. Returns true if a transaction commit was started.
    */
    int __jbd2_log_start_commit(journal_t *journal, tid_t target)
    {
    @@ -498,7 +498,8 @@ int jbd2_journal_force_commit_nested(jou

    /*
    * Start a commit of the current running transaction (if any). Returns true
    - * if a transaction was started, and fills its tid in at *ptid
    + * if a transaction is going to be committed (or is currently already
    + * committing), and fills its tid in at *ptid
    */
    int jbd2_journal_start_commit(journal_t *journal, tid_t *ptid)
    {
    @@ -508,15 +509,19 @@ int jbd2_journal_start_commit(journal_t
    if (journal->j_running_transaction) {
    tid_t tid = journal->j_running_transaction->t_tid;

    - ret = __jbd2_log_start_commit(journal, tid);
    - if (ret && ptid)
    + __jbd2_log_start_commit(journal, tid);
    + /* There's a running transaction and we've just made sure
    + * it's commit has been scheduled. */
    + if (ptid)
    *ptid = tid;
    - } else if (journal->j_committing_transaction && ptid) {
    + ret = 1;
    + } else if (journal->j_committing_transaction) {
    /*
    * If ext3_write_super() recently started a commit, then we
    * have to wait for completion of that transaction
    */
    - *ptid = journal->j_committing_transaction->t_tid;
    + if (ptid)
    + *ptid = journal->j_committing_transaction->t_tid;
    ret = 1;
    }
    spin_unlock(&journal->j_state_lock);



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