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| author | Li Zefan <lizefan@huawei.com> | 2014-02-27 18:19:03 +0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2014-02-27 09:35:59 -0500 |
| commit | 4729583006772b9530404bc1bb7c3aa4a10ffd4d (patch) | |
| tree | 06b53d469d09463d7c06dd9440870e84ced7b46c /kernel/cpuset.c | |
| parent | 532de3fc72adc2a6525c4d53c07bf81e1732083d (diff) | |
| download | lwn-4729583006772b9530404bc1bb7c3aa4a10ffd4d.tar.gz lwn-4729583006772b9530404bc1bb7c3aa4a10ffd4d.zip | |
cpuset: fix a locking issue in cpuset_migrate_mm()
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 from migrating to another
cpuset, 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: <stable@vger.kernel.org> # 3.9+
Signed-off-by: Li Zefan <lizefan@huawei.com>
Sigend-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cpuset.c')
| -rw-r--r-- | kernel/cpuset.c | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 4410ac6a55f1..dba9e4aef69a 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -974,12 +974,6 @@ 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 @@ -996,8 +990,10 @@ 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(); } /* |