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    Subject[PATCH 3/7] GFS2: Fix panic in glock memory shrinker
    Date
    From: Benjamin Marzinski <bmarzins@redhat.com>

    It is possible for gfs2_shrink_glock_memory() to check a glock for
    demotion
    that's in the process of being freed by gfs2_glock_put(). In this case,
    gfs2_shrink_glock_memory() will acquire a new reference to this glock,
    and
    then try to free the glock itself when it drops the refernce. To solve
    this, gfs2_shrink_glock_memory() just needs to check if the glock is in
    the process of being freed, and if so skip it without ever unlocking the
    lru_lock.

    Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
    Acked-by: Bob Peterson <rpeterso@redhat.com>
    Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
    ---
    fs/gfs2/glock.c | 4 ++++
    1 files changed, 4 insertions(+), 0 deletions(-)

    diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
    index fdb796c..827136e 100644
    --- a/fs/gfs2/glock.c
    +++ b/fs/gfs2/glock.c
    @@ -1314,6 +1314,10 @@ static int gfs2_shrink_glock_memory(int nr, gfp_t gfp_mask)
    list_del_init(&gl->gl_lru);
    atomic_dec(&lru_count);

    + /* Check if glock is about to be freed */
    + if (atomic_read(&gl->gl_ref) == 0)
    + continue;
    +
    /* Test for being demotable */
    if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
    gfs2_glock_hold(gl);
    --
    1.6.2.2


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