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Subject[PATCH] cpuset: avoid changing cpuset's cpus when -errno returned
After the patch:

commit 0b2f630a28d53b5a2082a5275bc3334b10373508
Author: Miao Xie <miaox@cn.fujitsu.com>
Date: Fri Jul 25 01:47:21 2008 -0700

cpusets: restructure the function update_cpumask() and update_nodemask()

It might happen that 'echo 0 > /cpuset/sub/cpus' returns failure but 'cpus'
has been changed, because cpus was changed before calling heap_init() which
may return -ENOMEM.

This patch restores the orginal behavior.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
kernel/cpuset.c | 32 ++++++++++++++------------------
1 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d5ab79c..817f8ac 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -774,36 +774,27 @@ static void cpuset_change_cpumask(struct task_struct *tsk,
/**
* update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
* @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
+ * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
*
* Called with cgroup_mutex held
*
* The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
* calling callback functions for each.
*
- * Return 0 if successful, -errno if not.
+ * Always return 0 if @heap != NULL, may return -errno if @heap == NULL
*/
-static int update_tasks_cpumask(struct cpuset *cs)
+static int update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
{
struct cgroup_scanner scan;
- struct ptr_heap heap;
int retval;

- /*
- * cgroup_scan_tasks() will initialize heap->gt for us.
- * heap_init() is still needed here for we should not change
- * cs->cpus_allowed when heap_init() fails.
- */
- retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
- if (retval)
- return retval;
-
scan.cg = cs->css.cgroup;
scan.test_task = cpuset_test_cpumask;
scan.process_task = cpuset_change_cpumask;
- scan.heap = &heap;
+ scan.heap = heap;
retval = cgroup_scan_tasks(&scan);
+ BUG_ON(heap != NULL && retval);

- heap_free(&heap);
return retval;
}

@@ -814,6 +805,7 @@ static int update_tasks_cpumask(struct cpuset *cs)
*/
static int update_cpumask(struct cpuset *cs, const char *buf)
{
+ struct ptr_heap heap;
struct cpuset trialcs;
int retval;
int is_load_balanced;
@@ -848,6 +840,10 @@ static int update_cpumask(struct cpuset *cs, const char *buf)
if (cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed))
return 0;

+ retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
+ if (retval)
+ return retval;
+
is_load_balanced = is_sched_load_balance(&trialcs);

mutex_lock(&callback_mutex);
@@ -858,9 +854,9 @@ static int update_cpumask(struct cpuset *cs, const char *buf)
* Scan tasks in the cpuset, and update the cpumasks of any
* that need an update.
*/
- retval = update_tasks_cpumask(cs);
- if (retval < 0)
- return retval;
+ update_tasks_cpumask(cs, &heap);
+
+ heap_free(&heap);

if (is_load_balanced)
rebuild_sched_domains();
@@ -1896,7 +1892,7 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
nodes_empty(cp->mems_allowed))
remove_tasks_in_empty_cpuset(cp);
else {
- update_tasks_cpumask(cp);
+ update_tasks_cpumask(cp, NULL);
update_tasks_nodemask(cp, &oldmems);
}
}
--
1.5.4.rc3



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