block-6.5-2023-07-21

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Merge tag 'block-6.5-2023-07-21' of git://git.kernel.dk/linux

Pull block fixes from Jens Axboe:

 - Fix for loop regressions (Mauricio)

 - Fix a potential stall with batched wakeups in sbitmap (David)

 - Fix for stall with recursive plug flushes (Ross)

 - Skip accounting of empty requests for blk-iocost (Chengming)

 - Remove a dead field in struct blk_mq_hw_ctx (Chengming)

* tag 'block-6.5-2023-07-21' of git://git.kernel.dk/linux:
  loop: do not enforce max_loop hard limit by (new) default
  loop: deprecate autoloading callback loop_probe()
  sbitmap: fix batching wakeup
  blk-iocost: skip empty flush bio in iocost
  blk-mq: delete dead struct blk_mq_hw_ctx->queued field
  blk-mq: Fix stall due to recursive flush plug

block/blk-core.c

@@ -1144,8 +1144,7 @@ void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
 {
 	if (!list_empty(&plug->cb_list))
 		flush_plug_callbacks(plug, from_schedule);
-	if (!rq_list_empty(plug->mq_list))
-		blk_mq_flush_plug_list(plug, from_schedule);
+	blk_mq_flush_plug_list(plug, from_schedule);
 	/*
 	 * Unconditionally flush out cached requests, even if the unplug
 	 * event came from schedule. Since we know hold references to the

block/blk-iocost.c

@@ -2516,6 +2516,10 @@ static void calc_vtime_cost_builtin(struct bio *bio, struct ioc_gq *iocg,
 	u64 seek_pages = 0;
 	u64 cost = 0;
 
+	/* Can't calculate cost for empty bio */
+	if (!bio->bi_iter.bi_size)
+		goto out;
+
 	switch (bio_op(bio)) {
 	case REQ_OP_READ:
 		coef_seqio	= ioc->params.lcoefs[LCOEF_RSEQIO];

block/blk-mq.c

@@ -2754,7 +2754,14 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
 	struct request *rq;
 
-	if (rq_list_empty(plug->mq_list))
+	/*
+	 * We may have been called recursively midway through handling
+	 * plug->mq_list via a schedule() in the driver's queue_rq() callback.
+	 * To avoid mq_list changing under our feet, clear rq_count early and
+	 * bail out specifically if rq_count is 0 rather than checking
+	 * whether the mq_list is empty.
+	 */
+	if (plug->rq_count == 0)
 		return;
 	plug->rq_count = 0;
 

drivers/block/loop.c

@@ -1775,14 +1775,43 @@ static const struct block_device_operations lo_fops = {
 /*
  * If max_loop is specified, create that many devices upfront.
  * This also becomes a hard limit. If max_loop is not specified,
+ * the default isn't a hard limit (as before commit 85c50197716c
+ * changed the default value from 0 for max_loop=0 reasons), just
  * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module
  * init time. Loop devices can be requested on-demand with the
  * /dev/loop-control interface, or be instantiated by accessing
  * a 'dead' device node.
  */
 static int max_loop = CONFIG_BLK_DEV_LOOP_MIN_COUNT;
-module_param(max_loop, int, 0444);
+
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
+static bool max_loop_specified;
+
+static int max_loop_param_set_int(const char *val,
+				  const struct kernel_param *kp)
+{
+	int ret;
+
+	ret = param_set_int(val, kp);
+	if (ret < 0)
+		return ret;
+
+	max_loop_specified = true;
+	return 0;
+}
+
+static const struct kernel_param_ops max_loop_param_ops = {
+	.set = max_loop_param_set_int,
+	.get = param_get_int,
+};
+
+module_param_cb(max_loop, &max_loop_param_ops, &max_loop, 0444);
 MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
+#else
+module_param(max_loop, int, 0444);
+MODULE_PARM_DESC(max_loop, "Initial number of loop devices");
+#endif
+
 module_param(max_part, int, 0444);
 MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device");
 
@@ -2093,14 +2122,18 @@ static void loop_remove(struct loop_device *lo)
 	put_disk(lo->lo_disk);
 }
 
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
 static void loop_probe(dev_t dev)
 {
 	int idx = MINOR(dev) >> part_shift;
 
-	if (max_loop && idx >= max_loop)
+	if (max_loop_specified && max_loop && idx >= max_loop)
 		return;
 	loop_add(idx);
 }
+#else
+#define loop_probe NULL
+#endif /* !CONFIG_BLOCK_LEGACY_AUTOLOAD */
 
 static int loop_control_remove(int idx)
 {
@@ -2281,6 +2314,9 @@ module_exit(loop_exit);
 static int __init max_loop_setup(char *str)
 {
 	max_loop = simple_strtol(str, NULL, 0);
+#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD
+	max_loop_specified = true;
+#endif
 	return 1;
 }
 

include/linux/blk-mq.h

@@ -397,8 +397,6 @@ struct blk_mq_hw_ctx {
 	 */
 	struct blk_mq_tags	*sched_tags;
 
-	/** @queued: Number of queued requests. */
-	unsigned long		queued;
 	/** @run: Number of dispatched requests. */
 	unsigned long		run;
 

lib/sbitmap.c

@@ -550,7 +550,7 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
 
 static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
 {
-	int i, wake_index;
+	int i, wake_index, woken;
 
 	if (!atomic_read(&sbq->ws_active))
 		return;
@@ -567,13 +567,12 @@ static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
 		 */
 		wake_index = sbq_index_inc(wake_index);
 
-		/*
-		 * It is sufficient to wake up at least one waiter to
-		 * guarantee forward progress.
-		 */
-		if (waitqueue_active(&ws->wait) &&
-		    wake_up_nr(&ws->wait, nr))
-			break;
+		if (waitqueue_active(&ws->wait)) {
+			woken = wake_up_nr(&ws->wait, nr);
+			if (woken == nr)
+				break;
+			nr -= woken;
+		}
 	}
 
 	if (wake_index != atomic_read(&sbq->wake_index))