Commit 3d2af77e authored by Waiman Long's avatar Waiman Long Committed by Jens Axboe
Browse files

blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats() 



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 3b8cc629 ("blk-cgroup:
Optimize blkcg_rstat_flush()") while the later one was introduced by
commit f7331648 ("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: 3b8cc629 ("blk-cgroup: Optimize blkcg_rstat_flush()")
Fixes: f7331648 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230606180724.2455066-1-longman@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a7cfa0af

block/blk-cgroup.c

+5 −0
Original line number Diff line number Diff line
@@ -610,8 +610,13 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css, 
			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);



		for (i = 0; i < BLKCG_MAX_POLS; i++) {

			struct blkcg_policy *pol = blkcg_policy[i];