cpusets: update_cpumask revision

Use the new function cgroup_scan_tasks() to step through all tasks in a
cpuset.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Cliff Wickman <cpw@sgi.com>
Cc: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 46 insertions, 61 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d94a8f7c4c29..20cb3916c66c 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -38,7 +38,6 @@
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/pagemap.h>
-#include <linux/prio_heap.h>
 #include <linux/proc_fs.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
@@ -740,22 +739,50 @@ static inline int started_after(void *p1, void *p2)
         return started_after_time(t1, &t2->start_time, t2);
 }
 
-/*
+/**
+ * cpuset_test_cpumask - test a task's cpus_allowed versus its cpuset's
+ * @tsk: task to test
+ * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
+ *
  * Call with manage_mutex held.  May take callback_mutex during call.
+ * Called for each task in a cgroup by cgroup_scan_tasks().
+ * Return nonzero if this tasks's cpus_allowed mask should be changed (in other
+ * words, if its mask is not equal to its cpuset's mask).
  */
+int cpuset_test_cpumask(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+        return !cpus_equal(tsk->cpus_allowed,
+                        (cgroup_cs(scan->cg))->cpus_allowed);
+}
 
+/**
+ * cpuset_change_cpumask - make a task's cpus_allowed the same as its cpuset's
+ * @tsk: task to test
+ * @scan: struct cgroup_scanner containing the cgroup of the task
+ *
+ * Called by cgroup_scan_tasks() for each task in a cgroup whose
+ * cpus_allowed mask needs to be changed.
+ *
+ * We don't need to re-check for the cgroup/cpuset membership, since we're
+ * holding cgroup_lock() at this point.
+ */
+void cpuset_change_cpumask(struct task_struct *tsk, struct cgroup_scanner *scan)
+{
+        set_cpus_allowed(tsk, (cgroup_cs(scan->cg))->cpus_allowed);
+}
+
+/**
+ * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
+ * @cs: the cpuset to consider
+ * @buf: buffer of cpu numbers written to this cpuset
+ */
 static int update_cpumask(struct cpuset *cs, char *buf)
 {
         struct cpuset trialcs;
-        int retval, i;
-        int is_load_balanced;
-        struct cgroup_iter it;
-        struct cgroup *cgrp = cs->css.cgroup;
-        struct task_struct *p, *dropped;
-        /* Never dereference latest_task, since it's not refcounted */
-        struct task_struct *latest_task = NULL;
+        struct cgroup_scanner scan;
         struct ptr_heap heap;
-        struct timespec latest_time = { 0, 0 };
+        int retval;
+        int is_load_balanced;
 
         /* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
         if (cs == &top_cpuset)
@@ -764,7 +791,7 @@ static int update_cpumask(struct cpuset *cs, char *buf)
         trialcs = *cs;
 
         /*
-         * An empty cpus_allowed is ok iff there are no tasks in the cpuset.
+         * An empty cpus_allowed is ok if there are no tasks in the cpuset.
          * Since cpulist_parse() fails on an empty mask, we special case
          * that parsing.  The validate_change() call ensures that cpusets
          * with tasks have cpus.
@@ -785,6 +812,7 @@ static int update_cpumask(struct cpuset *cs, char *buf)
         /* Nothing to do if the cpus didn't change */
         if (cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed))
                 return 0;
+
         retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, &started_after);
         if (retval)
                 return retval;
@@ -795,62 +823,19 @@ static int update_cpumask(struct cpuset *cs, char *buf)
         cs->cpus_allowed = trialcs.cpus_allowed;
         mutex_unlock(&callback_mutex);
 
- again:
         /*
          * Scan tasks in the cpuset, and update the cpumasks of any
-         * that need an update. Since we can't call set_cpus_allowed()
-         * while holding tasklist_lock, gather tasks to be processed
-         * in a heap structure. If the statically-sized heap fills up,
-         * overflow tasks that started later, and in future iterations
-         * only consider tasks that started after the latest task in
-         * the previous pass. This guarantees forward progress and
-         * that we don't miss any tasks
+         * that need an update.
          */
-        heap.size = 0;
-        cgroup_iter_start(cgrp, &it);
-        while ((p = cgroup_iter_next(cgrp, &it))) {
-                /* Only affect tasks that don't have the right cpus_allowed */
-                if (cpus_equal(p->cpus_allowed, cs->cpus_allowed))
-                        continue;
-                /*
-                 * Only process tasks that started after the last task
-                 * we processed
-                 */
-                if (!started_after_time(p, &latest_time, latest_task))
-                        continue;
-                dropped = heap_insert(&heap, p);
-                if (dropped == NULL) {
-                        get_task_struct(p);
-                } else if (dropped != p) {
-                        get_task_struct(p);
-                        put_task_struct(dropped);
-                }
-        }
-        cgroup_iter_end(cgrp, &it);
-        if (heap.size) {
-                for (i = 0; i < heap.size; i++) {
-                        struct task_struct *p = heap.ptrs[i];
-                        if (i == 0) {
-                                latest_time = p->start_time;
-                                latest_task = p;
-                        }
-                        set_cpus_allowed(p, cs->cpus_allowed);
-                        put_task_struct(p);
-                }
-                /*
-                 * If we had to process any tasks at all, scan again
-                 * in case some of them were in the middle of forking
-                 * children that didn't notice the new cpumask
-                 * restriction.  Not the most efficient way to do it,
-                 * but it avoids having to take callback_mutex in the
-                 * fork path
-                 */
-                goto again;
-        }
+        scan.cg = cs->css.cgroup;
+        scan.test_task = cpuset_test_cpumask;
+        scan.process_task = cpuset_change_cpumask;
+        scan.heap = &heap;
+        cgroup_scan_tasks(&scan);
         heap_free(&heap);
+
         if (is_load_balanced)
                 rebuild_sched_domains();
-
         return 0;
 }