[PATCH v2 1/4] cpuset: Remove unneeded NODEMASK_ALLOC() in cpuset_sprintf_memlist()

[PATCH v2 1/4] cpuset: Remove unneeded NODEMASK_ALLOC() in cpuset_sprintf_memlist()

[Li Zefan]

It's not necessary to copy cpuset->mems_allowed to a buffer
allocated by NODEMASK_ALLOC(). Just pass it to nodelist_scnprintf().

As spotted by Paul, a side effect is we fix a bug that the function
can return -ENOMEM but the caller doesn't expect negative return
value. Therefore change the return value of cpuset_sprintf_cpulist()
and cpuset_sprintf_memlist() from int to size_t.

Acked-by: Paul Menage <menage@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cpuset.c |   24 ++++++++----------------
 1 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 10f1835..e79650b 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1607,34 +1607,26 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
  * across a page fault.
  */
 
-static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
+static size_t cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
 {
-	int ret;
+	size_t count;
 
 	mutex_lock(&callback_mutex);
-	ret = cpulist_scnprintf(page, PAGE_SIZE, cs->cpus_allowed);
+	count = cpulist_scnprintf(page, PAGE_SIZE, cs->cpus_allowed);
 	mutex_unlock(&callback_mutex);
 
-	return ret;
+	return count;
 }
 
-static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
+static size_t cpuset_sprintf_memlist(char *page, struct cpuset *cs)
 {
-	NODEMASK_ALLOC(nodemask_t, mask, GFP_KERNEL);
-	int retval;
-
-	if (mask == NULL)
-		return -ENOMEM;
+	size_t count;
 
 	mutex_lock(&callback_mutex);
-	*mask = cs->mems_allowed;
+	count = nodelist_scnprintf(page, PAGE_SIZE, cs->mems_allowed);
 	mutex_unlock(&callback_mutex);
 
-	retval = nodelist_scnprintf(page, PAGE_SIZE, *mask);
-
-	NODEMASK_FREE(mask);
-
-	return retval;
+	return count;
 }
 
 static ssize_t cpuset_common_file_read(struct cgroup *cont,
-- 
1.7.3.1

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[PATCH v2 2/4] cpuset: Remove unneeded NODEMASK_ALLOC() in cpuset_attch()

[Li Zefan]

The variable 'from' is not modified after it's copied from
oldcs->mems_allowed, so we can just pass oldcs->mems_allowed
to cpuset_migrate_mm().

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cpuset.c |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index e79650b..8fef8c6 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1438,10 +1438,9 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 	struct mm_struct *mm;
 	struct cpuset *cs = cgroup_cs(cont);
 	struct cpuset *oldcs = cgroup_cs(oldcont);
-	NODEMASK_ALLOC(nodemask_t, from, GFP_KERNEL);
 	NODEMASK_ALLOC(nodemask_t, to, GFP_KERNEL);
 
-	if (from == NULL || to == NULL)
+	if (to == NULL)
 		goto alloc_fail;
 
 	if (cs == &top_cpuset) {
@@ -1463,18 +1462,16 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 	}
 
 	/* change mm; only needs to be done once even if threadgroup */
-	*from = oldcs->mems_allowed;
 	*to = cs->mems_allowed;
 	mm = get_task_mm(tsk);
 	if (mm) {
 		mpol_rebind_mm(mm, to);
 		if (is_memory_migrate(cs))
-			cpuset_migrate_mm(mm, from, to);
+			cpuset_migrate_mm(mm, &oldcs->mems_allowed, to);
 		mmput(mm);
 	}
 
 alloc_fail:
-	NODEMASK_FREE(from);
 	NODEMASK_FREE(to);
 }
 
-- 
1.7.3.1

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[PATCH v2 3/4] cpuset: Fix unchecked calls to NODEMASK_ALLOC()

[Li Zefan]

Those functions that use NODEMASK_ALLOC() can't propogate errno
to users, so might fail silently.

Fix it by using a static nodemask_t variable for each function, and
those variables are protected by cgroup_mutex;

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cpuset.c |   51 ++++++++++++++++-----------------------------------
 1 files changed, 16 insertions(+), 35 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 8fef8c6..3f93e5a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1015,17 +1015,12 @@ static void cpuset_change_nodemask(struct task_struct *p,
 	struct cpuset *cs;
 	int migrate;
 	const nodemask_t *oldmem = scan->data;
-	NODEMASK_ALLOC(nodemask_t, newmems, GFP_KERNEL);
-
-	if (!newmems)
-		return;
+	static nodemask_t newmems;	/* protected by cgroup_mutex */
 
 	cs = cgroup_cs(scan->cg);
-	guarantee_online_mems(cs, newmems);
+	guarantee_online_mems(cs, &newmems);
 
-	cpuset_change_task_nodemask(p, newmems);
-
-	NODEMASK_FREE(newmems);
+	cpuset_change_task_nodemask(p, &newmems);
 
 	mm = get_task_mm(p);
 	if (!mm)
@@ -1438,41 +1433,35 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 	struct mm_struct *mm;
 	struct cpuset *cs = cgroup_cs(cont);
 	struct cpuset *oldcs = cgroup_cs(oldcont);
-	NODEMASK_ALLOC(nodemask_t, to, GFP_KERNEL);
-
-	if (to == NULL)
-		goto alloc_fail;
+	static nodemask_t to;		/* protected by cgroup_mutex */
 
 	if (cs == &top_cpuset) {
 		cpumask_copy(cpus_attach, cpu_possible_mask);
 	} else {
 		guarantee_online_cpus(cs, cpus_attach);
 	}
-	guarantee_online_mems(cs, to);
+	guarantee_online_mems(cs, &to);
 
 	/* do per-task migration stuff possibly for each in the threadgroup */
-	cpuset_attach_task(tsk, to, cs);
+	cpuset_attach_task(tsk, &to, cs);
 	if (threadgroup) {
 		struct task_struct *c;
 		rcu_read_lock();
 		list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
-			cpuset_attach_task(c, to, cs);
+			cpuset_attach_task(c, &to, cs);
 		}
 		rcu_read_unlock();
 	}
 
 	/* change mm; only needs to be done once even if threadgroup */
-	*to = cs->mems_allowed;
+	to = cs->mems_allowed;
 	mm = get_task_mm(tsk);
 	if (mm) {
-		mpol_rebind_mm(mm, to);
+		mpol_rebind_mm(mm, &to);
 		if (is_memory_migrate(cs))
-			cpuset_migrate_mm(mm, &oldcs->mems_allowed, to);
+			cpuset_migrate_mm(mm, &oldcs->mems_allowed, &to);
 		mmput(mm);
 	}
-
-alloc_fail:
-	NODEMASK_FREE(to);
 }
 
 /* The various types of files and directories in a cpuset file system */
@@ -2051,10 +2040,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
 	struct cpuset *cp;	/* scans cpusets being updated */
 	struct cpuset *child;	/* scans child cpusets of cp */
 	struct cgroup *cont;
-	NODEMASK_ALLOC(nodemask_t, oldmems, GFP_KERNEL);
-
-	if (oldmems == NULL)
-		return;
+	static nodemask_t oldmems;	/* protected by cgroup_mutex */
 
 	list_add_tail((struct list_head *)&root->stack_list, &queue);
 
@@ -2071,7 +2057,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
 		    nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
 			continue;
 
-		*oldmems = cp->mems_allowed;
+		oldmems = cp->mems_allowed;
 
 		/* Remove offline cpus and mems from this cpuset. */
 		mutex_lock(&callback_mutex);
@@ -2087,10 +2073,9 @@ 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, NULL);
+			update_tasks_nodemask(cp, &oldmems, NULL);
 		}
 	}
-	NODEMASK_FREE(oldmems);
 }
 
 /*
@@ -2132,19 +2117,16 @@ void cpuset_update_active_cpus(void)
 static int cpuset_track_online_nodes(struct notifier_block *self,
 				unsigned long action, void *arg)
 {
-	NODEMASK_ALLOC(nodemask_t, oldmems, GFP_KERNEL);
-
-	if (oldmems == NULL)
-		return NOTIFY_DONE;
+	static nodemask_t oldmems;	/* protected by cgroup_mutex */
 
 	cgroup_lock();
 	switch (action) {
 	case MEM_ONLINE:
-		*oldmems = top_cpuset.mems_allowed;
+		oldmems = top_cpuset.mems_allowed;
 		mutex_lock(&callback_mutex);
 		top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
 		mutex_unlock(&callback_mutex);
-		update_tasks_nodemask(&top_cpuset, oldmems, NULL);
+		update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
 		break;
 	case MEM_OFFLINE:
 		/*
@@ -2158,7 +2140,6 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
 	}
 	cgroup_unlock();
 
-	NODEMASK_FREE(oldmems);
 	return NOTIFY_OK;
 }
 #endif
-- 
1.7.3.1

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[PATCH v2 4/4] cpuset: Hold callback_mutex in cpuset_clone()

[Li Zefan]

Chaning cpuset->mems/cpuset->cpus should be protected under
callback_mutex.

cpuset_post_clone() doesn't follow this rule. It's ok because it's
called when creating/initializing a cgroup, but we'd better
hold the lock to avoid subtil break in the future.

Acked-by: Paul Menage <menage@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/cpuset.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3f93e5a..1ca786a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1836,8 +1836,10 @@ static void cpuset_post_clone(struct cgroup_subsys *ss,
 	cs = cgroup_cs(cgroup);
 	parent_cs = cgroup_cs(parent);
 
+	mutex_lock(&callback_mutex);
 	cs->mems_allowed = parent_cs->mems_allowed;
 	cpumask_copy(cs->cpus_allowed, parent_cs->cpus_allowed);
+	mutex_unlock(&callback_mutex);
 	return;
 }
 
-- 
1.7.3.1

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