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>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 9 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index dca455e0482e..3778a21a4662 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;
 }
@@ -2003,7 +2010,7 @@ 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);
                 }
         }
 }