On Tue, Mar 28, 2017 at 11:43:04AM +0800, Ming Lei wrote:

On Mon, Mar 27, 2017 at 10:43:59AM -0700, Omar Sandoval wrote:

quoted

From: Omar Sandoval <redacted>

CONFIG_DEBUG_TEST_DRIVER_REMOVE found a possible leak of q->rq_wb in a
couple of cases: when a request queue is reregistered and when gendisks
share a request_queue. This has been a problem since wbt was introduced,
but the WARN_ON(!list_empty(&stats->callbacks)) in the blk-stat rework
exposed it. The fix is unfortunately a hack until we fix all of the
drivers sharing a request_queue.

Fixes: 87760e5eef35 ("block: hook up writeback throttling")
Signed-off-by: Omar Sandoval <redacted>
---
 block/blk-sysfs.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index fa831cb2fc30..a187e3f70028 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c

@@ -893,7 +893,21 @@ int blk_register_queue(struct gendisk *disk)
 
 	kobject_uevent(&q->kobj, KOBJ_ADD);
 
-	blk_wb_init(q);
+	/*
+	 * There are two cases where wbt may have already been initialized:
+	 * 1. A call sequence of blk_register_queue(); blk_unregister_queue();
+	 *    blk_register_queue().
+	 * 2. Multiple gendisks sharing a request_queue.
+	 *
+	 * To fix case 1, we'd like to call wbt_exit() in
+	 * blk_unregister_queue(). However, that's unsafe for case 2. So, we're
+	 * forced to do this and call wbt_exit() in blk_release_queue() instead.
+	 *
+	 * Note that in case 2, wbt will account across disks until those legacy
+	 * drivers are fixed.
+	 */
+	if (!q->rq_wb)
+		blk_wb_init(q);

Since 'rq_wb' is per-queue and its life time is same with queue's, I
am wondering why blk_wb_init() isn't put into blk_alloc_queue_node() or
queue's initialization api(blk_init_allocated_queue(), or
blk_mq_init_allocated_queue())?

Doing it at queue init time might be cleaner, I'll try that.