[PATCH 5.15 178/206] blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

Greg Kroah-Hartman
2026-02-04T15:01:22Z

From: Waiman Long <longman@redhat.com>

[ Upstream commit 3d2af77e31ade05ff7ccc3658c3635ec1bea0979 ]

When blkg_alloc() is called to allocate a blkcg_gq structure
with the associated blkg_iostat_set's, there are 2 fields within
blkg_iostat_set that requires proper initialization - blkg & sync.
The former field was introduced by commit 3b8cc6298724 ("blk-cgroup:
Optimize blkcg_rstat_flush()") while the later one was introduced by
commit f73316482977 ("blk-cgroup: reimplement basic IO stats using
cgroup rstat").

Unfortunately those fields in the blkg_iostat_set's are not properly
re-initialized when they are cleared in v1's blkcg_reset_stats(). This
can lead to a kernel panic due to NULL pointer access of the blkg
pointer. The missing initialization of sync is less problematic and
can be a problem in a debug kernel due to missing lockdep initialization.

Fix these problems by re-initializing them after memory clearing.

Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230606180724.2455066-1-longman@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[ Remove this line: bis -> blkg = blkg for blkg was introduced by commit
3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") since v6.2. ]
Signed-off-by: Alva Lan <alvalan9@foxmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
block/blk-cgroup.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -491,8 +491,12 @@ static int blkcg_reset_stats(struct cgro
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);
}
memset(&blkg->iostat, 0, sizeof(blkg->iostat));
+ u64_stats_init(&blkg->iostat.sync);

for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];