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    Subject[PATCH 4.2.y-ckt 188/218] sunrpc/cache: drop reference when sunrpc_cache_pipe_upcall() detects a race
    Date
    4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: NeilBrown <neilb@suse.com>

    commit a6ab1e8126d205238defbb55d23661a3a5c6a0d8 upstream.

    sunrpc_cache_pipe_upcall() can detect a race if CACHE_PENDING is no longer
    set. In this case it aborts the queuing of the upcall.
    However it has already taken a new counted reference on "h" and
    doesn't "put" it, even though it frees the data structure holding the reference.

    So let's delay the "cache_get" until we know we need it.

    Fixes: f9e1aedc6c79 ("sunrpc/cache: remove races with queuing an upcall.")
    Signed-off-by: NeilBrown <neilb@suse.com>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    net/sunrpc/cache.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
    index 8d79e70..9ec709b 100644
    --- a/net/sunrpc/cache.c
    +++ b/net/sunrpc/cache.c
    @@ -1175,14 +1175,14 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
    }

    crq->q.reader = 0;
    - crq->item = cache_get(h);
    crq->buf = buf;
    crq->len = 0;
    crq->readers = 0;
    spin_lock(&queue_lock);
    - if (test_bit(CACHE_PENDING, &h->flags))
    + if (test_bit(CACHE_PENDING, &h->flags)) {
    + crq->item = cache_get(h);
    list_add_tail(&crq->q.list, &detail->queue);
    - else
    + } else
    /* Lost a race, no longer PENDING, so don't enqueue */
    ret = -EAGAIN;
    spin_unlock(&queue_lock);
    --
    2.7.4
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