From a063057d7c731cffa7d10740e8ebc2970df8dbb3 Mon Sep 17 00:00:00 2001 From: Bart Van Assche Date: Wed, 28 Feb 2018 10:15:33 -0800 Subject: [PATCH] block: Fix a race between request queue removal and the block cgroup controller Avoid that the following race can occur: blk_cleanup_queue() blkcg_print_blkgs() spin_lock_irq(lock) (1) spin_lock_irq(blkg->q->queue_lock) (2,5) q->queue_lock = &q->__queue_lock (3) spin_unlock_irq(lock) (4) spin_unlock_irq(blkg->q->queue_lock) (6) (1) take driver lock; (2) busy loop for driver lock; (3) override driver lock with internal lock; (4) unlock driver lock; (5) can take driver lock now; (6) but unlock internal lock. This change is safe because only the SCSI core and the NVME core keep a reference on a request queue after having called blk_cleanup_queue(). Neither driver accesses any of the removed data structures between its blk_cleanup_queue() and blk_put_queue() calls. Reported-by: Joseph Qi Signed-off-by: Bart Van Assche Reviewed-by: Joseph Qi Cc: Jan Kara Signed-off-by: Jens Axboe --- block/blk-core.c | 31 +++++++++++++++++++++++++++++++ block/blk-sysfs.c | 7 ------- 2 files changed, 31 insertions(+), 7 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index 41c74b37be85..6febc69a58aa 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -719,6 +719,37 @@ void blk_cleanup_queue(struct request_queue *q) del_timer_sync(&q->backing_dev_info->laptop_mode_wb_timer); blk_sync_queue(q); + /* + * I/O scheduler exit is only safe after the sysfs scheduler attribute + * has been removed. + */ + WARN_ON_ONCE(q->kobj.state_in_sysfs); + + /* + * Since the I/O scheduler exit code may access cgroup information, + * perform I/O scheduler exit before disassociating from the block + * cgroup controller. + */ + if (q->elevator) { + ioc_clear_queue(q); + elevator_exit(q, q->elevator); + q->elevator = NULL; + } + + /* + * Remove all references to @q from the block cgroup controller before + * restoring @q->queue_lock to avoid that restoring this pointer causes + * e.g. blkcg_print_blkgs() to crash. + */ + blkcg_exit_queue(q); + + /* + * Since the cgroup code may dereference the @q->backing_dev_info + * pointer, only decrease its reference count after having removed the + * association with the block cgroup controller. + */ + bdi_put(q->backing_dev_info); + if (q->mq_ops) blk_mq_free_queue(q); percpu_ref_exit(&q->q_usage_counter); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index cbea895a5547..fd71a00c9462 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -798,13 +798,6 @@ static void __blk_release_queue(struct work_struct *work) if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags)) blk_stat_remove_callback(q, q->poll_cb); blk_stat_free_callback(q->poll_cb); - bdi_put(q->backing_dev_info); - blkcg_exit_queue(q); - - if (q->elevator) { - ioc_clear_queue(q); - elevator_exit(q, q->elevator); - } blk_free_queue_stats(q->stats);