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    Subject[PATCH 3.18 15/67] bcache: check ca->alloc_thread initialized before wake up it
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Coly Li <colyli@suse.de>

    commit 91af8300d9c1d7c6b6a2fd754109e08d4798b8d8 upstream.

    In bcache code, sysfs entries are created before all resources get
    allocated, e.g. allocation thread of a cache set.

    There is posibility for NULL pointer deference if a resource is accessed
    but which is not initialized yet. Indeed Jorg Bornschein catches one on
    cache set allocation thread and gets a kernel oops.

    The reason for this bug is, when bch_bucket_alloc() is called during
    cache set registration and attaching, ca->alloc_thread is not properly
    allocated and initialized yet, call wake_up_process() on ca->alloc_thread
    triggers NULL pointer deference failure. A simple and fast fix is, before
    waking up ca->alloc_thread, checking whether it is allocated, and only
    wake up ca->alloc_thread when it is not NULL.

    Signed-off-by: Coly Li <colyli@suse.de>
    Reported-by: Jorg Bornschein <jb@capsec.org>
    Cc: Kent Overstreet <kent.overstreet@gmail.com>
    Reviewed-by: Michael Lyle <mlyle@lyle.org>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/bcache/alloc.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/md/bcache/alloc.c
    +++ b/drivers/md/bcache/alloc.c
    @@ -406,7 +406,8 @@ long bch_bucket_alloc(struct cache *ca,

    finish_wait(&ca->set->bucket_wait, &w);
    out:
    - wake_up_process(ca->alloc_thread);
    + if (ca->alloc_thread)
    + wake_up_process(ca->alloc_thread);

    trace_bcache_alloc(ca, reserve);


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