Patch "blk-cgroup: fix list corruption from resetting io stat" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    blk-cgroup: fix list corruption from resetting io stat

to the 6.8-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:
     blk-cgroup-fix-list-corruption-from-resetting-io-sta.patch
and it can be found in the queue-6.8 subdirectory.

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



commit c5fc1ef40c90e825b12dea6928f83c5ef180ed12
Author: Ming Lei <ming.lei@xxxxxxxxxx>
Date:   Wed May 15 09:31:56 2024 +0800

    blk-cgroup: fix list corruption from resetting io stat
    
    [ Upstream commit 6da6680632792709cecf2b006f2fe3ca7857e791 ]
    
    Since commit 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()"),
    each iostat instance is added to blkcg percpu list, so blkcg_reset_stats()
    can't reset the stat instance by memset(), otherwise the llist may be
    corrupted.
    
    Fix the issue by only resetting the counter part.
    
    Cc: Tejun Heo <tj@xxxxxxxxxx>
    Cc: Waiman Long <longman@xxxxxxxxxx>
    Cc: Jay Shin <jaeshin@xxxxxxxxxx>
    Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
    Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
    Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240515013157.443672-2-ming.lei@xxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 4529122e0cbdb..98bd30114043e 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -619,12 +619,45 @@ static void blkg_destroy_all(struct gendisk *disk)
 	spin_unlock_irq(&q->queue_lock);
 }
 
+static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
+{
+	int i;
+
+	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
+		dst->bytes[i] = src->bytes[i];
+		dst->ios[i] = src->ios[i];
+	}
+}
+
+static void __blkg_clear_stat(struct blkg_iostat_set *bis)
+{
+	struct blkg_iostat cur = {0};
+	unsigned long flags;
+
+	flags = u64_stats_update_begin_irqsave(&bis->sync);
+	blkg_iostat_set(&bis->cur, &cur);
+	blkg_iostat_set(&bis->last, &cur);
+	u64_stats_update_end_irqrestore(&bis->sync, flags);
+}
+
+static void blkg_clear_stat(struct blkcg_gq *blkg)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct blkg_iostat_set *s = per_cpu_ptr(blkg->iostat_cpu, cpu);
+
+		__blkg_clear_stat(s);
+	}
+	__blkg_clear_stat(&blkg->iostat);
+}
+
 static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 			     struct cftype *cftype, u64 val)
 {
 	struct blkcg *blkcg = css_to_blkcg(css);
 	struct blkcg_gq *blkg;
-	int i, cpu;
+	int i;
 
 	mutex_lock(&blkcg_pol_mutex);
 	spin_lock_irq(&blkcg->lock);
@@ -635,18 +668,7 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 	 * anyway.  If you get hit by a race, retry.
 	 */
 	hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
-		for_each_possible_cpu(cpu) {
-			struct blkg_iostat_set *bis =
-				per_cpu_ptr(blkg->iostat_cpu, cpu);
-			memset(bis, 0, sizeof(*bis));
-
-			/* Re-initialize the cleared blkg_iostat_set */
-			u64_stats_init(&bis->sync);
-			bis->blkg = blkg;
-		}
-		memset(&blkg->iostat, 0, sizeof(blkg->iostat));
-		u64_stats_init(&blkg->iostat.sync);
-
+		blkg_clear_stat(blkg);
 		for (i = 0; i < BLKCG_MAX_POLS; i++) {
 			struct blkcg_policy *pol = blkcg_policy[i];
 
@@ -949,16 +971,6 @@ void blkg_conf_exit(struct blkg_conf_ctx *ctx)
 }
 EXPORT_SYMBOL_GPL(blkg_conf_exit);
 
-static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
-{
-	int i;
-
-	for (i = 0; i < BLKG_IOSTAT_NR; i++) {
-		dst->bytes[i] = src->bytes[i];
-		dst->ios[i] = src->ios[i];
-	}
-}
-
 static void blkg_iostat_add(struct blkg_iostat *dst, struct blkg_iostat *src)
 {
 	int i;