blk-cgroup: fix list corruption from resetting io stat

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@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Jay Shin <jaeshin@redhat.com>
Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20240515013157.443672-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 4b1a35ab0ea4c9c73a910a8c7454bb9ca2229881..8699f193cf315dbe668794a2aba0c77a6696a675 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -618,12 +618,45 @@ restart:
        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);
@@ -634,18 +667,7 @@ 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];
 
@@ -948,16 +970,6 @@ 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;