Hi Bart, On 18/2/1 07:53, Bart Van Assche wrote: > 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(). > - 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. > I'm afraid the risk may also exist in blk_cleanup_queue, which will set queue_lock to to the default internal lock. spin_lock_irq(lock); if (q->queue_lock != &q->__queue_lock) q->queue_lock = &q->__queue_lock; spin_unlock_irq(lock); I'm thinking of getting blkg->q->queue_lock to local first, but this will result in still using driver lock even the queue_lock has already been set to the default internal lock. Thanks, Joseph
