When cgroup_kn_lock_live() is called through some kernfs operation and
another thread is calling cgroup_rmdir(), we may trigger the warning in
cgroup_get().
------------[ cut here ]------------
WARNING: CPU: 1 PID: 1228 at kernel/cgroup.c:1034 cgroup_get+0x89/0xa0()
...
Call Trace:
[<c16ee73d>] dump_stack+0x41/0x52
[<c10468ef>] warn_slowpath_common+0x7f/0xa0
[<c104692d>] warn_slowpath_null+0x1d/0x20
[<c10bb999>] cgroup_get+0x89/0xa0
[<c10bbe58>] cgroup_kn_lock_live+0x28/0x70
[<c10be3c1>] __cgroup_procs_write.isra.26+0x51/0x230
[<c10be5b2>] cgroup_tasks_write+0x12/0x20
[<c10bb7b0>] cgroup_file_write+0x40/0x130
[<c11aee71>] kernfs_fop_write+0xd1/0x160
[<c1148e58>] vfs_write+0x98/0x1e0
[<c114934d>] SyS_write+0x4d/0xa0
[<c16f656b>] sysenter_do_call+0x12/0x12
---[ end trace 6f2e0c38c2108a74 ]---
Fix this by calling css_tryget() instead of cgroup_get().
Reported-by: Toralf Förster <toralf.foerster@xxxxxx>
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
---
kernel/cgroup.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e03fc62..c8d07e5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1025,6 +1025,11 @@ static umode_t cgroup_file_mode(const struct cftype *cft)
return mode;
}
+static bool cgroup_tryget(struct cgroup *cgrp)
+{
+ return css_tryget(&cgrp->self);
+}
+
static void cgroup_get(struct cgroup *cgrp)
{
WARN_ON_ONCE(cgroup_is_dead(cgrp));
@@ -1091,7 +1096,8 @@ static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn)
* protection against removal. Ensure @cgrp stays accessible and
* break the active_ref protection.
*/
- cgroup_get(cgrp);
+ if (!cgroup_tryget(cgrp))
+ return NULL;
kernfs_break_active_protection(kn);
mutex_lock(&cgroup_mutex);
--
1.8.0.2
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