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    Subject[v2.6.34-stable 180/213] ext4: limit group search loop for non-extent files
    Date
    From: Lachlan McIlroy <lmcilroy@redhat.com>

    -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
    -------------------

    commit e6155736ad76b2070652745f9e54cdea3f0d8567 upstream.

    In the case where we are allocating for a non-extent file,
    we must limit the groups we allocate from to those below
    2^32 blocks, and ext4_mb_regular_allocator() attempts to
    do this initially by putting a cap on ngroups for the
    subsequent search loop.

    However, the initial target group comes in from the
    allocation context (ac), and it may already be beyond
    the artificially limited ngroups. In this case,
    the limit

    if (group == ngroups)
    group = 0;

    at the top of the loop is never true, and the loop will
    run away.

    Catch this case inside the loop and reset the search to
    start at group 0.

    [sandeen@redhat.com: add commit msg & comments]

    Signed-off-by: Lachlan McIlroy <lmcilroy@redhat.com>
    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/mballoc.c | 6 +++++-
    1 file changed, 5 insertions(+), 1 deletion(-)

    diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
    index 5e440caf82de..ac7889907361 100644
    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -2068,7 +2068,11 @@ repeat:
    group = ac->ac_g_ex.fe_group;

    for (i = 0; i < ngroups; group++, i++) {
    - if (group == ngroups)
    + /*
    + * Artificially restricted ngroups for non-extent
    + * files makes group > ngroups possible on first loop.
    + */
    + if (group >= ngroups)
    group = 0;

    /* This now checks without needing the buddy page */
    --
    1.8.5.2


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