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    Subject[34-longterm 010/260] ext4: don't return to userspace after freezing the fs with a mutex held
    Date
    From: Eric Sandeen <sandeen@redhat.com>

    commit 6b0310fbf087ad6e9e3b8392adca97cd77184084 upstream.

    ext4_freeze() used jbd2_journal_lock_updates() which takes
    the j_barrier mutex, and then returns to userspace. The
    kernel does not like this:

    ================================================
    [ BUG: lock held when returning to user space! ]
    ------------------------------------------------
    lvcreate/1075 is leaving the kernel with locks still held!
    1 lock held by lvcreate/1075:
    #0: (&journal->j_barrier){+.+...}, at: [<ffffffff811c6214>]
    jbd2_journal_lock_updates+0xe1/0xf0

    Use vfs_check_frozen() added to ext4_journal_start_sb() and
    ext4_force_commit() instead.

    Addresses-Red-Hat-Bugzilla: #568503

    Signed-off-by: Eric Sandeen <sandeen@redhat.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    fs/ext4/super.c | 20 ++++++++++----------
    1 files changed, 10 insertions(+), 10 deletions(-)

    diff --git a/fs/ext4/super.c b/fs/ext4/super.c
    index e14d22c..00d09f5 100644
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -241,6 +241,7 @@ handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
    if (sb->s_flags & MS_RDONLY)
    return ERR_PTR(-EROFS);

    + vfs_check_frozen(sb, SB_FREEZE_WRITE);
    /* Special case here: if the journal has aborted behind our
    * backs (eg. EIO in the commit thread), then we still need to
    * take the FS itself readonly cleanly. */
    @@ -3485,8 +3486,10 @@ int ext4_force_commit(struct super_block *sb)
    return 0;

    journal = EXT4_SB(sb)->s_journal;
    - if (journal)
    + if (journal) {
    + vfs_check_frozen(sb, SB_FREEZE_WRITE);
    ret = ext4_journal_force_commit(journal);
    + }

    return ret;
    }
    @@ -3535,18 +3538,16 @@ static int ext4_freeze(struct super_block *sb)
    * the journal.
    */
    error = jbd2_journal_flush(journal);
    - if (error < 0) {
    - out:
    - jbd2_journal_unlock_updates(journal);
    - return error;
    - }
    + if (error < 0)
    + goto out;

    /* Journal blocked and flushed, clear needs_recovery flag. */
    EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
    error = ext4_commit_super(sb, 1);
    - if (error)
    - goto out;
    - return 0;
    +out:
    + /* we rely on s_frozen to stop further updates */
    + jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
    + return error;
    }

    /*
    @@ -3563,7 +3564,6 @@ static int ext4_unfreeze(struct super_block *sb)
    EXT4_SET_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
    ext4_commit_super(sb, 1);
    unlock_super(sb);
    - jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
    return 0;
    }

    --
    1.7.3.3


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