Patch "blkcg: Drop unnecessary RCU read [un]locks from blkg_conf_prep/finish()" has been added to the 6.3-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blkcg: Drop unnecessary RCU read [un]locks from blkg_conf_prep/finish()

to the 6.3-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     blkcg-drop-unnecessary-rcu-read-un-locks-from-blkg_c.patch
and it can be found in the queue-6.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 448882aff59adf56490282387c8f02bc4a2b5097
Author: Tejun Heo <tj@xxxxxxxxxx>
Date:   Wed Apr 12 14:06:46 2023 -1000

    blkcg: Drop unnecessary RCU read [un]locks from blkg_conf_prep/finish()
    
    [ Upstream commit 83462a6c971cdc550475b672cf29bd3b53bedf84 ]
    
    Now that all RCU flavors have been combined either holding a spin lock,
    disabling irq or disabling preemption implies RCU read lock, so there's no
    need to use rcu_read_[un]lock() explicitly while holding queue_lock. This
    shouldn't cause any behavior changes.
    
    v2: Description updated. Leave __acquires/release on queue_lock alone.
    
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Link: https://lore.kernel.org/r/20230413000649.115785-2-tj@xxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Stable-dep-of: a13bd91be223 ("block/rq_qos: protect rq_qos apis with a new lock")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 581aa08e34a8e..b2bdf76ec931d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -716,12 +716,12 @@ struct block_device *blkcg_conf_open_bdev(char **inputp)
  *
  * Parse per-blkg config update from @input and initialize @ctx with the
  * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
- * part of @input following MAJ:MIN.  This function returns with RCU read
- * lock and queue lock held and must be paired with blkg_conf_finish().
+ * part of @input following MAJ:MIN.  This function returns with queue lock
+ * held and must be paired with blkg_conf_finish().
  */
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 		   char *input, struct blkg_conf_ctx *ctx)
-	__acquires(rcu) __acquires(&bdev->bd_queue->queue_lock)
+	__acquires(&bdev->bd_queue->queue_lock)
 {
 	struct block_device *bdev;
 	struct gendisk *disk;
@@ -743,7 +743,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 	if (ret)
 		goto fail;
 
-	rcu_read_lock();
 	spin_lock_irq(&q->queue_lock);
 
 	if (!blkcg_policy_enabled(q, pol)) {
@@ -772,7 +771,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 
 		/* Drop locks to do new blkg allocation with GFP_KERNEL. */
 		spin_unlock_irq(&q->queue_lock);
-		rcu_read_unlock();
 
 		new_blkg = blkg_alloc(pos, disk, GFP_KERNEL);
 		if (unlikely(!new_blkg)) {
@@ -786,7 +784,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 			goto fail_exit_queue;
 		}
 
-		rcu_read_lock();
 		spin_lock_irq(&q->queue_lock);
 
 		if (!blkcg_policy_enabled(q, pol)) {
@@ -822,7 +819,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 	radix_tree_preload_end();
 fail_unlock:
 	spin_unlock_irq(&q->queue_lock);
-	rcu_read_unlock();
 fail_exit_queue:
 	blk_queue_exit(q);
 fail:
@@ -849,10 +845,9 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep);
  * with blkg_conf_prep().
  */
 void blkg_conf_finish(struct blkg_conf_ctx *ctx)
-	__releases(&ctx->bdev->bd_queue->queue_lock) __releases(rcu)
+	__releases(&ctx->bdev->bd_queue->queue_lock)
 {
 	spin_unlock_irq(&bdev_get_queue(ctx->bdev)->queue_lock);
-	rcu_read_unlock();
 	blkdev_put_no_open(ctx->bdev);
 }
 EXPORT_SYMBOL_GPL(blkg_conf_finish);