在 2022/3/14 16:06, Greg Kroah-Hartman 写道:
On Tue, Mar 08, 2022 at 04:12:32PM +0100, Michal Koutný wrote:
Hello.
On Mon, Feb 28, 2022 at 06:24:07PM +0100, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
[...] cpuset_attach() cpu hotplug --------------------------- ---------------------- down_write(cpuset_rwsem) guarantee_online_cpus() // (load cpus_attach) sched_cpu_deactivate set_cpu_active() // will change cpu_active_mask set_cpus_allowed_ptr(cpus_attach) __set_cpus_allowed_ptr_locked() // (if the intersection of cpus_attach and cpu_active_mask is empty, will return -EINVAL) up_write(cpuset_rwsem) [...] --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1528,6 +1528,7 @@ static void cpuset_attach(struct cgroup_ cgroup_taskset_first(tset, &css); cs = css_cs(css);
- cpus_read_lock(); mutex_lock(&cpuset_mutex);
This backport (and possible older kernels) looks suspicious since it comes before commit d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when the locking order was: cpuset lock, cpus lock.
At the same time it also comes before commit 710da3c8ea7d ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()") v5.4-rc1~176^2~27 when neither __sched_setscheduler() cared and this race is similar. (The swapped locking may still conflict with rebuild_sched_domains() before d74b27d63a8b.)
Thanks for noticing this. What do you recommend to do to resolve this?
thanks,
hi, Please review the following patch to fix it.
thanks.
patch:
[PATCH] cpuset: Fix unsafe lock order between cpuset lock and cpus lock
The backport commit 4eec5fe1c680a ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug") looks suspicious since it comes before commit d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when the locking order was: cpuset lock, cpus lock.
Fix it with the correct locking order and reduce the cpus locking range because only set_cpus_allowed_ptr() needs the protection of cpus lock.
Fixes: 4eec5fe1c680a ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug") Reported-by: Michal Koutný mkoutny@suse.com Signed-off-by: Zhang Qiao zhangqiao22@huawei.com --- kernel/cgroup/cpuset.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d43d25acc..4e1c4232e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1528,9 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) cgroup_taskset_first(tset, &css); cs = css_cs(css);
- cpus_read_lock(); mutex_lock(&cpuset_mutex);
+ /* + * It should hold cpus lock because a cpu offline event can + * cause set_cpus_allowed_ptr() failed. + */ + cpus_read_lock(); /* prepare for attach */ if (cs == &top_cpuset) cpumask_copy(cpus_attach, cpu_possible_mask); @@ -1549,6 +1553,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to); cpuset_update_task_spread_flag(cs, task); } + cpus_read_unlock();
/* * Change mm for all threadgroup leaders. This is expensive and may @@ -1584,7 +1589,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) wake_up(&cpuset_attach_wq);
mutex_unlock(&cpuset_mutex); - cpus_read_unlock(); }
/* The various types of files and directories in a cpuset file system */ -- 2.18.0
greg k-h .