I can trigger a lockdep warning:
# mount -t cgroup -o cpuset xxx /cgroup
# mkdir /cgroup/cpuset
# mkdir /cgroup/tmp
# echo 0 > /cgroup/tmp/cpuset.cpus
# echo 0 > /cgroup/tmp/cpuset.mems
# echo 1 > /cgroup/tmp/cpuset.memory_migrate
# echo $$ > /cgroup/tmp/tasks
# echo 1 > /cgruop/tmp/cpuset.mems
===============================
[ INFO: suspicious RCU usage. ]
3.14.0-rc1-0.1-default+ #32 Not tainted
-------------------------------
include/linux/cgroup.h:682 suspicious rcu_dereference_check() usage!
...
[<ffffffff81582174>] dump_stack+0x72/0x86
[<ffffffff810b8f01>] lockdep_rcu_suspicious+0x101/0x140
[<ffffffff81105ba1>] cpuset_migrate_mm+0xb1/0xe0
...
We used to hold cgroup_mutex when calling cpuset_migrate_mm(), but now
we hold cpuset_mutex, which causes task_css() to complain.
This is not a false-positive but a real issue.
Holding cpuset_mutex won't prevent a task's cpuset from changing, and
it won't prevent the original task->cgroup from destroying during this
change.
Fixes: 5d21cc2db040 (cpuset: replace cgroup_mutex locking with cpuset internal locking)
Cc: <[email protected]> # 3.9+
Signed-off-by: Li Zefan <[email protected]>
---
kernel/cpuset.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d8bec21..5f50ec6 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -948,12 +948,6 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
* Temporarilly set tasks mems_allowed to target nodes of migration,
* so that the migration code can allocate pages on these nodes.
*
- * Call holding cpuset_mutex, so current's cpuset won't change
- * during this call, as manage_mutex holds off any cpuset_attach()
- * calls. Therefore we don't need to take task_lock around the
- * call to guarantee_online_mems(), as we know no one is changing
- * our task's cpuset.
- *
* While the mm_struct we are migrating is typically from some
* other task, the task_struct mems_allowed that we are hacking
* is for our current task, which must allocate new pages for that
@@ -970,8 +964,10 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
+ rcu_read_lock();
mems_cs = effective_nodemask_cpuset(task_cs(tsk));
guarantee_online_mems(mems_cs, &tsk->mems_allowed);
+ rcu_read_unlock();
}
/*
--
1.8.0.2
It's not safe to access task's cpuset after releasing task_lock().
Holding callback_mutex won't help.
Cc: <[email protected]>
Signed-off-by: Li Zefan <[email protected]>
---
kernel/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 5f50ec6..c63a0d9 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2412,9 +2412,9 @@ int __cpuset_node_allowed_softwall(int node, gfp_t gfp_mask)
task_lock(current);
cs = nearest_hardwall_ancestor(task_cs(current));
+ allowed = node_isset(node, cs->mems_allowed);
task_unlock(current);
- allowed = node_isset(node, cs->mems_allowed);
mutex_unlock(&callback_mutex);
return allowed;
}
--
1.8.0.2
On 2014/2/27 18:19, Li Zefan wrote:
> I can trigger a lockdep warning:
>
> # mount -t cgroup -o cpuset xxx /cgroup
> # mkdir /cgroup/cpuset
> # mkdir /cgroup/tmp
> # echo 0 > /cgroup/tmp/cpuset.cpus
> # echo 0 > /cgroup/tmp/cpuset.mems
> # echo 1 > /cgroup/tmp/cpuset.memory_migrate
> # echo $$ > /cgroup/tmp/tasks
> # echo 1 > /cgruop/tmp/cpuset.mems
>
> ===============================
> [ INFO: suspicious RCU usage. ]
> 3.14.0-rc1-0.1-default+ #32 Not tainted
> -------------------------------
> include/linux/cgroup.h:682 suspicious rcu_dereference_check() usage!
> ...
> [<ffffffff81582174>] dump_stack+0x72/0x86
> [<ffffffff810b8f01>] lockdep_rcu_suspicious+0x101/0x140
> [<ffffffff81105ba1>] cpuset_migrate_mm+0xb1/0xe0
> ...
>
> We used to hold cgroup_mutex when calling cpuset_migrate_mm(), but now
> we hold cpuset_mutex, which causes task_css() to complain.
>
> This is not a false-positive but a real issue.
>
> Holding cpuset_mutex won't prevent a task's cpuset from changing, and
I meant it won't prevent a task from migrating to another cpuset.
> it won't prevent the original task->cgroup from destroying during this
> change.
On Thu, Feb 27, 2014 at 06:19:03PM +0800, Li Zefan wrote:
> I can trigger a lockdep warning:
>
> # mount -t cgroup -o cpuset xxx /cgroup
> # mkdir /cgroup/cpuset
> # mkdir /cgroup/tmp
> # echo 0 > /cgroup/tmp/cpuset.cpus
> # echo 0 > /cgroup/tmp/cpuset.mems
> # echo 1 > /cgroup/tmp/cpuset.memory_migrate
> # echo $$ > /cgroup/tmp/tasks
> # echo 1 > /cgruop/tmp/cpuset.mems
>
> ===============================
> [ INFO: suspicious RCU usage. ]
> 3.14.0-rc1-0.1-default+ #32 Not tainted
> -------------------------------
> include/linux/cgroup.h:682 suspicious rcu_dereference_check() usage!
> ...
> [<ffffffff81582174>] dump_stack+0x72/0x86
> [<ffffffff810b8f01>] lockdep_rcu_suspicious+0x101/0x140
> [<ffffffff81105ba1>] cpuset_migrate_mm+0xb1/0xe0
> ...
>
> We used to hold cgroup_mutex when calling cpuset_migrate_mm(), but now
> we hold cpuset_mutex, which causes task_css() to complain.
>
> This is not a false-positive but a real issue.
>
> Holding cpuset_mutex won't prevent a task's cpuset from changing, and
> it won't prevent the original task->cgroup from destroying during this
> change.
>
> Fixes: 5d21cc2db040 (cpuset: replace cgroup_mutex locking with cpuset internal locking)
> Cc: <[email protected]> # 3.9+
> Signed-off-by: Li Zefan <[email protected]>
Applied to cgroup/for-3.14-fixes.
Thanks.
--
tejun
On Thu, Feb 27, 2014 at 06:19:36PM +0800, Li Zefan wrote:
> It's not safe to access task's cpuset after releasing task_lock().
> Holding callback_mutex won't help.
>
> Cc: <[email protected]>
> Signed-off-by: Li Zefan <[email protected]>
Applied to cgroup/for-3.14-fixes.
Thanks.
--
tejun