Re: data-race in cgroup_get_tree / proc_cgroup_show
From: Tejun Heo <tj@kernel.org>
Date: 2022-08-28 18:22:16
Also in:
bpf, cgroups, lkml
Subsystem:
control group (cgroup), the rest · Maintainers:
Tejun Heo, Johannes Weiner, Michal Koutný, Linus Torvalds
On Mon, Aug 22, 2022 at 01:04:58PM -0400, Gabriel Ryan wrote:
Hi Christian, We ran a quick test and confirm your suggestion would eliminate the data race alert we observed. If the data race is benign (and it appears to be), using WRITE_ONCE(cgrp_dfl_visible, true) instead of cmpxchg in cgroup_get_tree() would probably also be ok.
I don't see how the data race can lead to anything but would the following work? Thanks.
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ffaccd6373f1e..a90fdba881bdb 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c@@ -2172,7 +2172,7 @@ static int cgroup_get_tree(struct fs_context *fc) struct cgroup_fs_context *ctx = cgroup_fc2context(fc); int ret; - cgrp_dfl_visible = true; + WRITE_ONCE(cgrp_dfl_visible, true); cgroup_get_live(&cgrp_dfl_root.cgrp); ctx->root = &cgrp_dfl_root;
@@ -6056,7 +6056,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns, struct cgroup *cgrp; int ssid, count = 0; - if (root == &cgrp_dfl_root && !cgrp_dfl_visible) + if (root == &cgrp_dfl_root && !READ_ONCE(cgrp_dfl_visible)) continue; seq_printf(m, "%d:", root->hierarchy_id);
--
tejun