From: Tejun Heo tj@kernel.org
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@kernel.org Reviewed-and-tested-by: Imran Khan imran.f.khan@oracle.com Reported-and-tested-by: Xuewen Yan xuewen.yan@unisoc.com Fixes: 05c7b7a92cc8 ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug") Cc: stable@vger.kernel.org # v5.17+ Signed-off-by: Cai Xinchen caixinchen1@huawei.com --- 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 */