The commit is pushed to "branch-rh10-6.12.0-211.16.1.12.x.vz10-ovz" and will
appear at [email protected]:openvz/vzkernel.git
after rh10-6.12.0-211.16.1.el10
------>
commit 59dac0d1c38ebfb91fcb2472deed5ddca6dac841
Author: Konstantin Khorenko <[email protected]>
Date: Thu Jun 4 00:03:34 2026 +0200
cgroup-v2/freezer: avoid sleeping allocations under RCU in freeze-timeout
warning
warn_freeze_timeout() holds guard(rcu)() for its whole body (required by
css_for_each_descendant_post()) and, inside that, both
warn_freeze_timeout_task() and the "no unfreezable process" tail do
kmalloc(PATH_MAX / stack-trace buffer, GFP_KERNEL). GFP_KERNEL may sleep,
which is illegal inside an RCU read-side critical section ("sleeping
function called from invalid context", caught by
CONFIG_DEBUG_ATOMIC_SLEEP). The path is reachable from
cgroup.events show -> check_freeze_timeout() -> warn_freeze_timeout() when
a freeze exceeds sysctl_freeze_timeout and passes the ratelimit.
The non-allocating work here (cgroup_path(), stack_trace_save_tsk()) is
atomic-safe; only the allocations sleep. Use GFP_ATOMIC for the three
buffers - this is a rare, ratelimited diagnostic path with small
(<=PATH_MAX)
allocations, so the stricter allocation context is acceptable.
Fixes: e4bcc416ab19 ("cgroup-v2/freezer: Print information about
unfreezable process")
https://virtuozzo.atlassian.net/browse/VSTOR-132310
Feature: cgroup/freeze: enhance logging
Signed-off-by: Konstantin Khorenko <[email protected]>
---
kernel/cgroup/cgroup.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 347b3761c37b..78a02ea49e8c 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4129,7 +4129,13 @@ void warn_freeze_timeout_task(struct cgroup *cgrp, int
timeout,
unsigned long nr_entries, i;
pid_t tgid;
- buf = kmalloc(PATH_MAX, GFP_KERNEL);
+ /*
+ * Called from warn_freeze_timeout() under rcu_read_lock() (the
+ * css_for_each_descendant_post() iteration), so allocations here must
+ * not sleep. This is a rare, ratelimited diagnostic path with small
+ * buffers, so GFP_ATOMIC is fine.
+ */
+ buf = kmalloc(PATH_MAX, GFP_ATOMIC);
if (!buf)
return;
@@ -4142,7 +4148,7 @@ void warn_freeze_timeout_task(struct cgroup *cgrp, int
timeout,
buf, timeout/HZ, tgid, task->comm);
entries = kmalloc(MAX_STACK_TRACE_DEPTH * sizeof(*entries),
- GFP_KERNEL);
+ GFP_ATOMIC);
if (!entries)
return;
nr_entries = stack_trace_save_tsk(task, entries,
@@ -4176,7 +4182,8 @@ static void warn_freeze_timeout(struct cgroup *cgrp, int
timeout)
css_task_iter_end(&it);
}
- buf = kmalloc(PATH_MAX, GFP_KERNEL);
+ /* still under rcu_read_lock() from guard(rcu)() above */
+ buf = kmalloc(PATH_MAX, GFP_ATOMIC);
if (!buf)
return;
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