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Subject[PATCH 3/4] cpuset: avoid changing cpuset's mems when errno returned
When writing to cpuset.mems, cpuset has to update its mems_allowed before
calling update_tasks_nodemask(), but this function might return -ENOMEM.

To avoid this rare case, we allocate the memory before changing mems_allowed,
and then pass to update_tasks_nodemask(). Similar to what update_cpumask()
does.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
kernel/cpuset.c | 25 ++++++++++++++++---------
1 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 01a111f..3202364 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1057,13 +1057,15 @@ static void *cpuset_being_rebound;
* update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
* @cs: the cpuset in which each task's mems_allowed mask needs to be changed
* @oldmem: old mems_allowed of cpuset cs
+ * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
*
* Called with cgroup_mutex held
- * Return 0 if successful, -errno if not.
+ * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
+ * if @heap != NULL.
*/
-static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem)
+static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
+ struct ptr_heap *heap)
{
- int retval;
struct cgroup_scanner scan;

cpuset_being_rebound = cs; /* causes mpol_dup() rebind */
@@ -1071,7 +1073,7 @@ static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem)
scan.cg = cs->css.cgroup;
scan.test_task = NULL;
scan.process_task = cpuset_change_nodemask;
- scan.heap = NULL;
+ scan.heap = heap;
scan.data = (nodemask_t *)oldmem;

/*
@@ -1084,12 +1086,10 @@ static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem)
* It's ok if we rebind the same mm twice; mpol_rebind_mm()
* is idempotent. Also migrate pages in each mm to new nodes.
*/
- retval = cgroup_scan_tasks(&scan);
+ cgroup_scan_tasks(&scan);

/* We're done rebinding vmas to this cpuset's new mems_allowed. */
cpuset_being_rebound = NULL;
-
- return retval;
}

/*
@@ -1110,6 +1110,7 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
{
nodemask_t oldmem;
int retval;
+ struct ptr_heap heap;

/*
* top_cpuset.mems_allowed tracks node_stats[N_HIGH_MEMORY];
@@ -1144,12 +1145,18 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
if (retval < 0)
goto done;

+ retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
+ if (retval < 0)
+ goto done;
+
mutex_lock(&callback_mutex);
cs->mems_allowed = trialcs->mems_allowed;
cs->mems_generation = cpuset_mems_generation++;
mutex_unlock(&callback_mutex);

- retval = update_tasks_nodemask(cs, &oldmem);
+ update_tasks_nodemask(cs, &oldmem, &heap);
+
+ heap_free(&heap);
done:
return retval;
}
@@ -2002,7 +2009,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
remove_tasks_in_empty_cpuset(cp);
else {
update_tasks_cpumask(cp, NULL);
- update_tasks_nodemask(cp, &oldmems);
+ update_tasks_nodemask(cp, &oldmems, NULL);
}
}
}
-- 1.5.4.rc3

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