linux-kernel - [PATCH block/for-next] blk-cgroup: cgroup_rstat

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Message-ID: <20191114223128.GM4163745@devbig004.ftw2.facebook.com>
Date:   Thu, 14 Nov 2019 14:31:28 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Faiz Abbas <faiz_abbas@...com>, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        lizefan@...wei.com, hannes@...xchg.org, kernel-team@...com,
        Dan Schatzberg <dschatzberg@...com>, Daniel Xu <dlxu@...com>
Subject: [PATCH block/for-next] blk-cgroup: cgroup_rstat_updated() shouldn't
 be called on cgroup1

Currently, cgroup rstat is supported only on cgroup2 hierarchy and
rstat functions shouldn't be called on cgroup1 cgroups.  While
converting blk-cgroup core statistics to rstat, f73316482977
("blk-cgroup: reimplement basic IO stats using cgroup rstat")
accidentally ended up calling cgroup_rstat_updated() on cgroup1
cgroups causing crashes.

Longer term, we probably should add cgroup1 support to rstat but for
now let's mask the call directly.

Signed-off-by: Tejun Heo <tj@...nel.org>
Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
---
 include/linux/blk-cgroup.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 48a66738143d..19394c77ed99 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -626,7 +626,8 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 		bis->cur.ios[rwd]++;
 
 		u64_stats_update_end(&bis->sync);
-		cgroup_rstat_updated(blkg->blkcg->css.cgroup, cpu);
+		if (cgroup_subsys_on_dfl(io_cgrp_subsys))
+			cgroup_rstat_updated(blkg->blkcg->css.cgroup, cpu);
 		put_cpu();
 	}