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Message-Id: <20240703185229.1849423-1-longman@redhat.com>
Date: Wed, 3 Jul 2024 14:52:29 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>,
Zefan Li <lizefan.x@...edance.com>,
Johannes Weiner <hannes@...xchg.org>
Cc: cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org,
Waiman Long <longman@...hat.com>
Subject: [PATCH] cgroup: Protect css->cgroup write under css_set_lock
The writing of css->cgroup associated with the cgroup root in
rebind_subsystems() is currently protected only by cgroup_mutex.
However, the reading of css->cgroup in both proc_cpuset_show() and
proc_cgroup_show() is protected just by css_set_lock. That makes the
readers susceptible to racing problems like data tearing or caching.
It is also a problem that can be reported by KCSAN.
This can be fixed by using READ_ONCE() and WRITE_ONCE() to access
css->cgroup. Alternatively, the writing of css->cgroup can be moved
under css_set_lock as well which is done by this patch.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/cgroup/cgroup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ff3c14fa62e6..c8e4b62b436a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1842,9 +1842,9 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
rcu_assign_pointer(dcgrp->subsys[ssid], css);
ss->root = dst_root;
- css->cgroup = dcgrp;
spin_lock_irq(&css_set_lock);
+ css->cgroup = dcgrp;
WARN_ON(!list_empty(&dcgrp->e_csets[ss->id]));
list_for_each_entry_safe(cset, cset_pos, &scgrp->e_csets[ss->id],
e_cset_node[ss->id]) {
--
2.39.3
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