mm_owner_changed callback can also be called with new task set to NULL.
(race between try_to_unuse() and mm->owner exiting). Surprisingly the order
of cgroup arguments being passed was incorrect (proves that we did not
run into mm_owner_changed callback at all).

Signed-off-by: Balbir Singh
---

mm/memrlimitcgroup.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff -puN mm/memrlimitcgroup.c~memrlimit-handle-mm-owner-notification-with-task-null mm/memrlimitcgroup.c
--- linux-2.6.27-rc1/mm/memrlimitcgroup.c~memrlimit-handle-mm-owner-notification-with-task-null 2008-08-05 10:56:56.000000000 +0530
+++ linux-2.6.27-rc1-balbir/mm/memrlimitcgroup.c 2008-08-05 11:24:04.000000000 +0530
@@ -73,6 +73,12 @@ void memrlimit_cgroup_uncharge_as(struct
{
struct memrlimit_cgroup *memrcg;

+ /*
+ * Uncharge happened as a part of the mm_owner_changed callback
+ */
+ if (!mm->owner)
+ return;
+
memrcg = memrlimit_cgroup_from_task(mm->owner);
res_counter_uncharge(&memrcg->as_res, (nr_pages << PAGE_SHIFT));
}
@@ -235,8 +241,8 @@ out:
* This callback is called with mmap_sem held
*/
static void memrlimit_cgroup_mm_owner_changed(struct cgroup_subsys *ss,
- struct cgroup *cgrp,
struct cgroup *old_cgrp,
+ struct cgroup *cgrp,
struct task_struct *p)
{
struct memrlimit_cgroup *memrcg, *old_memrcg;
@@ -246,7 +252,12 @@ static void memrlimit_cgroup_mm_owner_ch
memrcg = memrlimit_cgroup_from_cgrp(cgrp);
old_memrcg = memrlimit_cgroup_from_cgrp(old_cgrp);

- if (res_counter_charge(&memrcg->as_res, (mm->total_vm << PAGE_SHIFT)))
+ /*
+ * If we don't have a new cgroup, we just uncharge from the old one.
+ * It means that the task is going away
+ */
+ if (memrcg &&
+ res_counter_charge(&memrcg->as_res, (mm->total_vm << PAGE_SHIFT)))
goto out;
res_counter_uncharge(&old_memrcg->as_res, (mm->total_vm << PAGE_SHIFT));
out:
_

--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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