On Mon, Jun 19, 2023 at 05:20:19PM +0800, Ming Lei wrote:
On Mon, Jun 19, 2023 at 10:51:16AM +0200, Greg Kroah-Hartman wrote:
On Mon, Jun 19, 2023 at 04:30:09PM +0800, Ming Lei wrote:
As noted by Michal, the blkg_iostat_set's in the lockless list hold reference to blkg's to protect against their removal. Those blkg's hold reference to blkcg. When a cgroup is being destroyed, cgroup_rstat_flush() is only called at css_release_work_fn() which is called when the blkcg reference count reaches 0. This circular dependency will prevent blkcg and some blkgs from being freed after they are made offline.
It is less a problem if the cgroup to be destroyed also has other controllers like memory that will call cgroup_rstat_flush() which will clean up the reference count. If block is the only controller that uses rstat, these offline blkcg and blkgs may never be freed leaking more and more memory over time.
To prevent this potential memory leak:
- flush blkcg per-cpu stats list in __blkg_release(), when no new stat
can be added
- add global blkg_stat_lock for covering concurrent parent blkg stat
update
- don't grab bio->bi_blkg reference when adding the stats into blkcg's
per-cpu stat list since all stats are guaranteed to be consumed before releasing blkg instance, and grabbing blkg reference for stats was the most fragile part of original patch
Based on Waiman's patch:
https://lore.kernel.org/linux-block/20221215033132.230023-3-longman@redhat.c...
Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") Cc: stable@vger.kernel.org Reported-by: Jay Shin jaeshin@redhat.com Acked-by: Tejun Heo tj@kernel.org Cc: Waiman Long longman@redhat.com Cc: mkoutny@suse.com Cc: Yosry Ahmed yosryahmed@google.com Signed-off-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20230609234249.1412858-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk
Context difference with linus tree: 2c275afeb61d ("block: make blkcg_punt_bio_submit optional") adds '#ifdef CONFIG_BLK_CGROUP_PUNT_BIO' in __blkg_release().
What is the git commit id of this change in Linus's tree?
20cb1c2fb756 ("blk-cgroup: Flush stats before releasing blkcg_gq")
Thanks, now queued up.
greg k-h