• Bart Van Assche's avatar
    block: Fix a race between the cgroup code and request queue initialization · 498f6650
    Bart Van Assche authored
    Initialize the request queue lock earlier such that the following
    race can no longer occur:
    
    blk_init_queue_node()             blkcg_print_blkgs()
      blk_alloc_queue_node (1)
        q->queue_lock = &q->__queue_lock (2)
        blkcg_init_queue(q) (3)
                                        spin_lock_irq(blkg->q->queue_lock) (4)
      q->queue_lock = lock (5)
                                        spin_unlock_irq(blkg->q->queue_lock) (6)
    
    (1) allocate an uninitialized queue;
    (2) initialize queue_lock to its default internal lock;
    (3) initialize blkcg part of request queue, which will create blkg and
        then insert it to blkg_list;
    (4) traverse blkg_list and find the created blkg, and then take its
        queue lock, here it is the default *internal lock*;
    (5) *race window*, now queue_lock is overridden with *driver specified
        lock*;
    (6) now unlock *driver specified lock*, not the locked *internal lock*,
        unlock balance breaks.
    
    The changes in this patch are as follows:
    - Move the .queue_lock initialization from blk_init_queue_node() into
      blk_alloc_queue_node().
    - Only override the .queue_lock pointer for legacy queues because it
      is not useful for blk-mq queues to override this pointer.
    - For all all block drivers that initialize .queue_lock explicitly,
      change the blk_alloc_queue() call in the driver into a
      blk_alloc_queue_node() call and remove the explicit .queue_lock
      initialization. Additionally, initialize the spin lock that will
      be used as queue lock earlier if necessary.
    Reported-by: default avatarJoseph Qi <joseph.qi@linux.alibaba.com>
    Signed-off-by: default avatarBart Van Assche <bart.vanassche@wdc.com>
    Reviewed-by: default avatarJoseph Qi <joseph.qi@linux.alibaba.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Philipp Reisner <philipp.reisner@linbit.com>
    Cc: Ulf Hansson <ulf.hansson@linaro.org>
    Cc: Kees Cook <keescook@chromium.org>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    498f6650
drbd_main.c 113 KB