block: add an explicit ->disk backpointer to the request_queue

Replace the magic lookup through the kobject tree with an explicit
backpointer, given that the device model links are set up and torn
down at times when I/O is still possible, leading to potential
NULL or invalid pointer dereferences.

Fixes: edb0872f44 ("block: move the bdi from the request_queue to the gendisk")
Reported-by: syzbot <syzbot+aa0801b6b32dca9dda82@syzkaller.appspotmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Sven Schnelle <svens@linux.ibm.com>
Link: https://lore.kernel.org/r/20210816134624.GA24234@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -5269,7 +5269,7 @@ bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
 	switch (ioprio_class) {
 	default:
 		pr_err("bdi %s: bfq: bad prio class %d\n",
-			bdi_dev_name(queue_to_disk(bfqq->bfqd->queue)->bdi),
+			bdi_dev_name(bfqq->bfqd->queue->disk->bdi),
 			ioprio_class);
 		fallthrough;
 	case IOPRIO_CLASS_NONE:

block/blk-cgroup.c

@@ -489,9 +489,9 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 
 const char *blkg_dev_name(struct blkcg_gq *blkg)
 {
-	if (!queue_has_disk(blkg->q) || !queue_to_disk(blkg->q)->bdi->dev)
+	if (!blkg->q->disk || !blkg->q->disk->bdi->dev)
 		return NULL;
-	return bdi_dev_name(queue_to_disk(blkg->q)->bdi);
+	return bdi_dev_name(blkg->q->disk->bdi);
 }
 
 /**

block/blk-mq.c

@@ -525,7 +525,7 @@ void blk_mq_free_request(struct request *rq)
 		__blk_mq_dec_active_requests(hctx);
 
 	if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
-		laptop_io_completion(queue_to_disk(q)->bdi);
+		laptop_io_completion(q->disk->bdi);
 
 	rq_qos_done(q, rq);
 

block/blk-settings.c

@@ -141,9 +141,9 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
 				 limits->logical_block_size >> SECTOR_SHIFT);
 	limits->max_sectors = max_sectors;
 
-	if (!queue_has_disk(q))
+	if (!q->disk)
 		return;
-	queue_to_disk(q)->bdi->io_pages = max_sectors >> (PAGE_SHIFT - 9);
+	q->disk->bdi->io_pages = max_sectors >> (PAGE_SHIFT - 9);
 }
 EXPORT_SYMBOL(blk_queue_max_hw_sectors);
 
@@ -475,9 +475,9 @@ EXPORT_SYMBOL(blk_limits_io_opt);
 void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
 {
 	blk_limits_io_opt(&q->limits, opt);
-	if (!queue_has_disk(q))
+	if (!q->disk)
 		return;
-	queue_to_disk(q)->bdi->ra_pages =
+	q->disk->bdi->ra_pages =
 		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
 }
 EXPORT_SYMBOL(blk_queue_io_opt);

block/blk-sysfs.c

@@ -90,9 +90,9 @@ static ssize_t queue_ra_show(struct request_queue *q, char *page)
 {
 	unsigned long ra_kb;
 
-	if (!queue_has_disk(q))
+	if (!q->disk)
 		return -EINVAL;
-	ra_kb = queue_to_disk(q)->bdi->ra_pages << (PAGE_SHIFT - 10);
+	ra_kb = q->disk->bdi->ra_pages << (PAGE_SHIFT - 10);
 	return queue_var_show(ra_kb, page);
 }
 
@@ -102,12 +102,12 @@ queue_ra_store(struct request_queue *q, const char *page, size_t count)
 	unsigned long ra_kb;
 	ssize_t ret;
 
-	if (!queue_has_disk(q))
+	if (!q->disk)
 		return -EINVAL;
 	ret = queue_var_store(&ra_kb, page, count);
 	if (ret < 0)
 		return ret;
-	queue_to_disk(q)->bdi->ra_pages = ra_kb >> (PAGE_SHIFT - 10);
+	q->disk->bdi->ra_pages = ra_kb >> (PAGE_SHIFT - 10);
 	return ret;
 }
 
@@ -254,9 +254,8 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 
 	spin_lock_irq(&q->queue_lock);
 	q->limits.max_sectors = max_sectors_kb << 1;
-	if (queue_has_disk(q))
-		queue_to_disk(q)->bdi->io_pages =
-			max_sectors_kb >> (PAGE_SHIFT - 10);
+	if (q->disk)
+		q->disk->bdi->io_pages = max_sectors_kb >> (PAGE_SHIFT - 10);
 	spin_unlock_irq(&q->queue_lock);
 
 	return ret;

block/blk-wbt.c

@@ -97,7 +97,7 @@ static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
  */
 static bool wb_recent_wait(struct rq_wb *rwb)
 {
-	struct bdi_writeback *wb = &queue_to_disk(rwb->rqos.q)->bdi->wb;
+	struct bdi_writeback *wb = &rwb->rqos.q->disk->bdi->wb;
 
 	return time_before(jiffies, wb->dirty_sleep + HZ);
 }
@@ -234,7 +234,7 @@ enum {
 
 static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
 {
-	struct backing_dev_info *bdi = queue_to_disk(rwb->rqos.q)->bdi;
+	struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
 	struct rq_depth *rqd = &rwb->rq_depth;
 	u64 thislat;
 
@@ -287,7 +287,7 @@ static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
 
 static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
 {
-	struct backing_dev_info *bdi = queue_to_disk(rwb->rqos.q)->bdi;
+	struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
 	struct rq_depth *rqd = &rwb->rq_depth;
 
 	trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,
@@ -359,8 +359,8 @@ static void wb_timer_fn(struct blk_stat_callback *cb)
 
 	status = latency_exceeded(rwb, cb->stat);
 
-	trace_wbt_timer(queue_to_disk(rwb->rqos.q)->bdi, status,
-			rqd->scale_step, inflight);
+	trace_wbt_timer(rwb->rqos.q->disk->bdi, status, rqd->scale_step,
+			inflight);
 
 	/*
 	 * If we exceeded the latency target, step down. If we did not,

block/genhd.c

@@ -1078,6 +1078,7 @@ static void disk_release(struct device *dev)
 	disk_release_events(disk);
 	kfree(disk->random);
 	xa_destroy(&disk->part_tbl);
+	disk->queue->disk = NULL;
 	blk_put_queue(disk->queue);
 	iput(disk->part0->bd_inode);	/* frees the disk */
 }
@@ -1276,6 +1277,7 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 	device_initialize(disk_to_dev(disk));
 	inc_diskseq(disk);
 	disk->queue = q;
+	q->disk = disk;
 	lockdep_init_map(&disk->lockdep_map, "(bio completion)", lkclass, 0);
 #ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
 	INIT_LIST_HEAD(&disk->slave_bdevs);

include/linux/blkdev.h

@@ -421,6 +421,8 @@ struct request_queue {
 
 	spinlock_t		queue_lock;
 
+	struct gendisk		*disk;
+
 	/*
 	 * queue kobject
 	 */
@@ -661,9 +663,6 @@ extern void blk_clear_pm_only(struct request_queue *q);
 	dma_map_page_attrs(dev, (bv)->bv_page, (bv)->bv_offset, (bv)->bv_len, \
 	(dir), (attrs))
 
-#define queue_has_disk(q)	((q)->kobj.parent != NULL)
-#define queue_to_disk(q)	(dev_to_disk(kobj_to_dev((q)->kobj.parent)))
-
 static inline bool queue_is_mq(struct request_queue *q)
 {
 	return q->mq_ops;

include/trace/events/kyber.h

@@ -30,7 +30,7 @@ TRACE_EVENT(kyber_latency,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= disk_devt(queue_to_disk(q));
+		__entry->dev		= disk_devt(q->disk);
 		strlcpy(__entry->domain, domain, sizeof(__entry->domain));
 		strlcpy(__entry->type, type, sizeof(__entry->type));
 		__entry->percentile	= percentile;
@@ -59,7 +59,7 @@ TRACE_EVENT(kyber_adjust,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= disk_devt(queue_to_disk(q));
+		__entry->dev		= disk_devt(q->disk);
 		strlcpy(__entry->domain, domain, sizeof(__entry->domain));
 		__entry->depth		= depth;
 	),
@@ -81,7 +81,7 @@ TRACE_EVENT(kyber_throttled,
 	),
 
 	TP_fast_assign(
-		__entry->dev		= disk_devt(queue_to_disk(q));
+		__entry->dev		= disk_devt(q->disk);
 		strlcpy(__entry->domain, domain, sizeof(__entry->domain));
 	),