From: Tejun Heo <tj@xxxxxxxxxx>
commit 4f7e7236435ca0abe005c674ebd6892c6e83aeb3 upstream.
Add #include <linux/cpu.h> to avoid compile error on some architectures.
commit 9a3284fad42f6 ("cgroup: Optimize single thread migration") and
commit 671c11f0619e5 ("cgroup: Elide write-locking threadgroup_rwsem
when updating csses on an empty subtree") are not backport. So ignore the
input parameter of cgroup_attach_lock/cgroup_attach_unlock.
original commit message:
Bringing up a CPU may involve creating and destroying tasks which requires
read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside
cpus_read_lock(). However, cpuset's ->attach(), which may be called with
thredagroup_rwsem write-locked, also wants to disable CPU hotplug and
acquires cpus_read_lock(), leading to a deadlock.
Fix it by guaranteeing that ->attach() is always called with CPU hotplug
disabled and removing cpus_read_lock() call from cpuset_attach().
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-and-tested-by: Imran Khan <imran.f.khan@xxxxxxxxxx>
Reported-and-tested-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
Fixes: 05c7b7a92cc8 ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug")
Cc: stable@xxxxxxxxxxxxxxx # v5.17+
Signed-off-by: Cai Xinchen <caixinchen1@xxxxxxxxxx>
---
v2:
- Add #include <linux/cpu.h> in kernel/cgroup/cgroup.c to avoid compile
error on some architectures
---
kernel/cgroup/cgroup.c | 50 +++++++++++++++++++++++++++++++++++++-----
kernel/cgroup/cpuset.c | 7 +-----
2 files changed, 46 insertions(+), 11 deletions(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index a892a99eb4bf..a8185cdb8587 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -55,6 +55,7 @@
#include <linux/nsproxy.h>
#include <linux/file.h>
#include <linux/sched/cputime.h>
+#include <linux/cpu.h>
#include <net/sock.h>
#define CREATE_TRACE_POINTS
@@ -2209,6 +2210,45 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
}
EXPORT_SYMBOL_GPL(task_cgroup_path);
+/**
+ * cgroup_attach_lock - Lock for ->attach()
+ * @lock_threadgroup: whether to down_write cgroup_threadgroup_rwsem
+ *
+ * cgroup migration sometimes needs to stabilize threadgroups against forks and
+ * exits by write-locking cgroup_threadgroup_rwsem. However, some ->attach()
+ * implementations (e.g. cpuset), also need to disable CPU hotplug.
+ * Unfortunately, letting ->attach() operations acquire cpus_read_lock() can
+ * lead to deadlocks.
+ *
+ * Bringing up a CPU may involve creating and destroying tasks which requires
+ * read-locking threadgroup_rwsem, so threadgroup_rwsem nests inside
+ * cpus_read_lock(). If we call an ->attach() which acquires the cpus lock while
+ * write-locking threadgroup_rwsem, the locking order is reversed and we end up
+ * waiting for an on-going CPU hotplug operation which in turn is waiting for
+ * the threadgroup_rwsem to be released to create new tasks. For more details:
+ *
+ * http://lkml.kernel.org/r/20220711174629.uehfmqegcwn2lqzu@wubuntu
+ *
+ * Resolve the situation by always acquiring cpus_read_lock() before optionally
+ * write-locking cgroup_threadgroup_rwsem. This allows ->attach() to assume that
+ * CPU hotplug is disabled on entry.
+ */
+static void cgroup_attach_lock(void)
+{
+ get_online_cpus();
+ percpu_down_write(&cgroup_threadgroup_rwsem);
+}
+
+/**
+ * cgroup_attach_unlock - Undo cgroup_attach_lock()
+ * @lock_threadgroup: whether to up_write cgroup_threadgroup_rwsem
+ */
+static void cgroup_attach_unlock(void)
+{
+ percpu_up_write(&cgroup_threadgroup_rwsem);
+ put_online_cpus();
+}
+
/**
* cgroup_migrate_add_task - add a migration target task to a migration context
* @task: target task
@@ -2694,7 +2734,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
return ERR_PTR(-EINVAL);
- percpu_down_write(&cgroup_threadgroup_rwsem);
+ cgroup_attach_lock();
rcu_read_lock();
if (pid) {
@@ -2725,7 +2765,7 @@ struct task_struct *cgroup_procs_write_start(char *buf, bool threadgroup)
goto out_unlock_rcu;
out_unlock_threadgroup:
- percpu_up_write(&cgroup_threadgroup_rwsem);
+ cgroup_attach_unlock();
out_unlock_rcu:
rcu_read_unlock();
return tsk;
@@ -2740,7 +2780,7 @@ void cgroup_procs_write_finish(struct task_struct *task)
/* release reference from cgroup_procs_write_start() */
put_task_struct(task);
- percpu_up_write(&cgroup_threadgroup_rwsem);
+ cgroup_attach_unlock();
for_each_subsys(ss, ssid)
if (ss->post_attach)
ss->post_attach();
@@ -2799,7 +2839,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
lockdep_assert_held(&cgroup_mutex);
- percpu_down_write(&cgroup_threadgroup_rwsem);
+ cgroup_attach_lock();
/* look up all csses currently attached to @cgrp's subtree */
spin_lock_irq(&css_set_lock);
@@ -2830,7 +2870,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
ret = cgroup_migrate_execute(&mgctx);
out_finish:
cgroup_migrate_finish(&mgctx);
- percpu_up_write(&cgroup_threadgroup_rwsem);
+ cgroup_attach_unlock();
return ret;
}
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7169e47fb48b..c6d412cebc43 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1528,11 +1528,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
cgroup_taskset_first(tset, &css);
cs = css_cs(css);
- /*
- * It should hold cpus lock because a cpu offline event can
- * cause set_cpus_allowed_ptr() failed.
- */
- get_online_cpus();
+ lockdep_assert_cpus_held(); /* see cgroup_attach_lock() */
mutex_lock(&cpuset_mutex);
/* prepare for attach */
@@ -1588,7 +1584,6 @@ static void cpuset_attach(struct cgroup_taskset *tset)
wake_up(&cpuset_attach_wq);
mutex_unlock(&cpuset_mutex);
- put_online_cpus();
}
/* The various types of files and directories in a cpuset file system */
--
2.17.1
