cpuset: don't allocate trial cpuset on stack

Impact: cleanups, reduce stack usage

This patch prepares for the next patch.  When we convert
cpuset.cpus_allowed to cpumask_var_t, (trialcs = *cs) no longer works.

Another result of this patch is reducing stack usage of trialcs.
sizeof(*cs) can be as large as 148 bytes on x86_64, so it's really not
good to have it on stack.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Mike Travis <travis@sgi.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 60 insertions, 33 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1e32e6b380af..f66527bfd216 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -415,6 +415,24 @@ static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
                 is_mem_exclusive(p) <= is_mem_exclusive(q);
 }
 
+/**
+ * alloc_trial_cpuset - allocate a trial cpuset
+ * @cs: the cpuset that the trial cpuset duplicates
+ */
+static struct cpuset *alloc_trial_cpuset(const struct cpuset *cs)
+{
+        return kmemdup(cs, sizeof(*cs), GFP_KERNEL);
+}
+
+/**
+ * free_trial_cpuset - free the trial cpuset
+ * @trial: the trial cpuset to be freed
+ */
+static void free_trial_cpuset(struct cpuset *trial)
+{
+        kfree(trial);
+}
+
 /*
  * validate_change() - Used to validate that any proposed cpuset change
  *                     follows the structural rules for cpusets.
@@ -880,10 +898,10 @@ static void update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
  * @cs: the cpuset to consider
  * @buf: buffer of cpu numbers written to this cpuset
  */
-static int update_cpumask(struct cpuset *cs, const char *buf)
+static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
+                          const char *buf)
 {
         struct ptr_heap heap;
-        struct cpuset trialcs;
         int retval;
         int is_load_balanced;
 
@@ -891,8 +909,6 @@ static int update_cpumask(struct cpuset *cs, const char *buf)
         if (cs == &top_cpuset)
                 return -EACCES;
 
-        trialcs = *cs;
-
         /*
          * An empty cpus_allowed is ok only if the cpuset has no tasks.
          * Since cpulist_parse() fails on an empty mask, we special case
@@ -900,31 +916,31 @@ static int update_cpumask(struct cpuset *cs, const char *buf)
          * with tasks have cpus.
          */
         if (!*buf) {
-                cpus_clear(trialcs.cpus_allowed);
+                cpus_clear(trialcs->cpus_allowed);
         } else {
-                retval = cpulist_parse(buf, &trialcs.cpus_allowed);
+                retval = cpulist_parse(buf, &trialcs->cpus_allowed);
                 if (retval < 0)
                         return retval;
 
-                if (!cpus_subset(trialcs.cpus_allowed, cpu_online_map))
+                if (!cpus_subset(trialcs->cpus_allowed, cpu_online_map))
                         return -EINVAL;
         }
-        retval = validate_change(cs, &trialcs);
+        retval = validate_change(cs, trialcs);
         if (retval < 0)
                 return retval;
 
         /* Nothing to do if the cpus didn't change */
-        if (cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed))
+        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);
+        is_load_balanced = is_sched_load_balance(trialcs);
 
         mutex_lock(&callback_mutex);
-        cs->cpus_allowed = trialcs.cpus_allowed;
+        cs->cpus_allowed = trialcs->cpus_allowed;
         mutex_unlock(&callback_mutex);
 
         /*
@@ -1099,9 +1115,9 @@ done:
  * lock each such tasks mm->mmap_sem, scan its vma's and rebind
  * their mempolicies to the cpusets new mems_allowed.
  */
-static int update_nodemask(struct cpuset *cs, const char *buf)
+static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
+                           const char *buf)
 {
-        struct cpuset trialcs;
         nodemask_t oldmem;
         int retval;
 
@@ -1112,8 +1128,6 @@ static int update_nodemask(struct cpuset *cs, const char *buf)
         if (cs == &top_cpuset)
                 return -EACCES;
 
-        trialcs = *cs;
-
         /*
          * An empty mems_allowed is ok iff there are no tasks in the cpuset.
          * Since nodelist_parse() fails on an empty mask, we special case
@@ -1121,27 +1135,27 @@ static int update_nodemask(struct cpuset *cs, const char *buf)
          * with tasks have memory.
          */
         if (!*buf) {
-                nodes_clear(trialcs.mems_allowed);
+                nodes_clear(trialcs->mems_allowed);
         } else {
-                retval = nodelist_parse(buf, trialcs.mems_allowed);
+                retval = nodelist_parse(buf, trialcs->mems_allowed);
                 if (retval < 0)
                         goto done;
 
-                if (!nodes_subset(trialcs.mems_allowed,
+                if (!nodes_subset(trialcs->mems_allowed,
                                 node_states[N_HIGH_MEMORY]))
                         return -EINVAL;
         }
         oldmem = cs->mems_allowed;
-        if (nodes_equal(oldmem, trialcs.mems_allowed)) {
+        if (nodes_equal(oldmem, trialcs->mems_allowed)) {
                 retval = 0;             /* Too easy - nothing to do */
                 goto done;
         }
-        retval = validate_change(cs, &trialcs);
+        retval = validate_change(cs, trialcs);
         if (retval < 0)
                 goto done;
 
         mutex_lock(&callback_mutex);
-        cs->mems_allowed = trialcs.mems_allowed;
+        cs->mems_allowed = trialcs->mems_allowed;
         cs->mems_generation = cpuset_mems_generation++;
         mutex_unlock(&callback_mutex);
 
@@ -1181,31 +1195,36 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
 static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
                        int turning_on)
 {
-        struct cpuset trialcs;
+        struct cpuset *trialcs;
         int err;
         int balance_flag_changed;
 
-        trialcs = *cs;
+        trialcs = alloc_trial_cpuset(cs);
+        if (!trialcs)
+                return -ENOMEM;
+
         if (turning_on)
-                set_bit(bit, &trialcs.flags);
+                set_bit(bit, &trialcs->flags);
         else
-                clear_bit(bit, &trialcs.flags);
+                clear_bit(bit, &trialcs->flags);
 
-        err = validate_change(cs, &trialcs);
+        err = validate_change(cs, trialcs);
         if (err < 0)
-                return err;
+                goto out;
 
         balance_flag_changed = (is_sched_load_balance(cs) !=
-                                        is_sched_load_balance(&trialcs));
+                                is_sched_load_balance(trialcs));
 
         mutex_lock(&callback_mutex);
-        cs->flags = trialcs.flags;
+        cs->flags = trialcs->flags;
         mutex_unlock(&callback_mutex);
 
-        if (!cpus_empty(trialcs.cpus_allowed) && balance_flag_changed)
+        if (!cpus_empty(trialcs->cpus_allowed) && balance_flag_changed)
                 async_rebuild_sched_domains();
 
-        return 0;
+out:
+        free_trial_cpuset(trialcs);
+        return err;
 }
 
 /*
@@ -1453,21 +1472,29 @@ static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
                                 const char *buf)
 {
         int retval = 0;
+        struct cpuset *cs = cgroup_cs(cgrp);
+        struct cpuset *trialcs;
 
         if (!cgroup_lock_live_group(cgrp))
                 return -ENODEV;
 
+        trialcs = alloc_trial_cpuset(cs);
+        if (!trialcs)
+                return -ENOMEM;
+
         switch (cft->private) {
         case FILE_CPULIST:
-                retval = update_cpumask(cgroup_cs(cgrp), buf);
+                retval = update_cpumask(cs, trialcs, buf);
                 break;
         case FILE_MEMLIST:
-                retval = update_nodemask(cgroup_cs(cgrp), buf);
+                retval = update_nodemask(cs, trialcs, buf);
                 break;
         default:
                 retval = -EINVAL;
                 break;
         }
+
+        free_trial_cpuset(trialcs);
         cgroup_unlock();
         return retval;
 }