Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched: arch_reinit_sched_domains() must destroy domains to force rebuild
  sched, cpuset: rework sched domains and CPU hotplug handling (v4)

1 files changed, 182 insertions, 130 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d5ab79cf516d..f227bc172690 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -14,6 +14,8 @@
  *  2003-10-22 Updates by Stephen Hemminger.
  *  2004 May-July Rework by Paul Jackson.
  *  2006 Rework by Paul Menage to use generic cgroups
+ *  2008 Rework of the scheduler domains and CPU hotplug handling
+ *       by Max Krasnyansky
  *
  *  This file is subject to the terms and conditions of the GNU General Public
  *  License.  See the file COPYING in the main directory of the Linux
@@ -236,9 +238,11 @@ static struct cpuset top_cpuset = {
 
 static DEFINE_MUTEX(callback_mutex);
 
-/* This is ugly, but preserves the userspace API for existing cpuset
+/*
+ * This is ugly, but preserves the userspace API for existing cpuset
  * users. If someone tries to mount the "cpuset" filesystem, we
- * silently switch it to mount "cgroup" instead */
+ * silently switch it to mount "cgroup" instead
+ */
 static int cpuset_get_sb(struct file_system_type *fs_type,
                          int flags, const char *unused_dev_name,
                          void *data, struct vfsmount *mnt)
@@ -473,10 +477,9 @@ static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
 }
 
 /*
- * Helper routine for rebuild_sched_domains().
+ * Helper routine for generate_sched_domains().
  * Do cpusets a, b have overlapping cpus_allowed masks?
  */
-
 static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
 {
         return cpus_intersects(a->cpus_allowed, b->cpus_allowed);
@@ -518,26 +521,15 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
 }
 
 /*
- * rebuild_sched_domains()
- *
- * This routine will be called to rebuild the scheduler's dynamic
- * sched domains:
- * - if the flag 'sched_load_balance' of any cpuset with non-empty
- *   'cpus' changes,
- * - or if the 'cpus' allowed changes in any cpuset which has that
- *   flag enabled,
- * - or if the 'sched_relax_domain_level' of any cpuset which has
- *   that flag enabled and with non-empty 'cpus' changes,
- * - or if any cpuset with non-empty 'cpus' is removed,
- * - or if a cpu gets offlined.
- *
- * This routine builds a partial partition of the systems CPUs
- * (the set of non-overlappping cpumask_t's in the array 'part'
- * below), and passes that partial partition to the kernel/sched.c
- * partition_sched_domains() routine, which will rebuild the
- * schedulers load balancing domains (sched domains) as specified
- * by that partial partition.  A 'partial partition' is a set of
- * non-overlapping subsets whose union is a subset of that set.
+ * generate_sched_domains()
+ *
+ * This function builds a partial partition of the systems CPUs
+ * A 'partial partition' is a set of non-overlapping subsets whose
+ * union is a subset of that set.
+ * The output of this function needs to be passed to kernel/sched.c
+ * partition_sched_domains() routine, which will rebuild the scheduler's
+ * load balancing domains (sched domains) as specified by that partial
+ * partition.
  *
  * See "What is sched_load_balance" in Documentation/cpusets.txt
  * for a background explanation of this.
@@ -547,13 +539,7 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
  * domains when operating in the severe memory shortage situations
  * that could cause allocation failures below.
  *
- * Call with cgroup_mutex held.  May take callback_mutex during
- * call due to the kfifo_alloc() and kmalloc() calls.  May nest
- * a call to the get_online_cpus()/put_online_cpus() pair.
- * Must not be called holding callback_mutex, because we must not
- * call get_online_cpus() while holding callback_mutex.  Elsewhere
- * the kernel nests callback_mutex inside get_online_cpus() calls.
- * So the reverse nesting would risk an ABBA deadlock.
+ * Must be called with cgroup_lock held.
  *
  * The three key local variables below are:
  *    q  - a linked-list queue of cpuset pointers, used to implement a
@@ -588,10 +574,10 @@ update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
  *      element of the partition (one sched domain) to be passed to
  *      partition_sched_domains().
  */
-
-void rebuild_sched_domains(void)
+static int generate_sched_domains(cpumask_t **domains,
+                        struct sched_domain_attr **attributes)
 {
-        LIST_HEAD(q);           /* queue of cpusets to be scanned*/
+        LIST_HEAD(q);           /* queue of cpusets to be scanned */
         struct cpuset *cp;      /* scans q */
         struct cpuset **csa;    /* array of all cpuset ptrs */
         int csn;                /* how many cpuset ptrs in csa so far */
@@ -601,23 +587,26 @@ void rebuild_sched_domains(void)
         int ndoms;              /* number of sched domains in result */
         int nslot;              /* next empty doms[] cpumask_t slot */
 
-        csa = NULL;
+        ndoms = 0;
         doms = NULL;
         dattr = NULL;
+        csa = NULL;
 
         /* Special case for the 99% of systems with one, full, sched domain */
         if (is_sched_load_balance(&top_cpuset)) {
-                ndoms = 1;
                 doms = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
                 if (!doms)
-                        goto rebuild;
+                        goto done;
+
                 dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
                 if (dattr) {
                         *dattr = SD_ATTR_INIT;
                         update_domain_attr_tree(dattr, &top_cpuset);
                 }
                 *doms = top_cpuset.cpus_allowed;
-                goto rebuild;
+
+                ndoms = 1;
+                goto done;
         }
 
         csa = kmalloc(number_of_cpusets * sizeof(cp), GFP_KERNEL);
@@ -680,61 +669,141 @@ restart:
                 }
         }
 
-        /* Convert <csn, csa> to <ndoms, doms> */
+        /*
+         * Now we know how many domains to create.
+         * Convert <csn, csa> to <ndoms, doms> and populate cpu masks.
+         */
         doms = kmalloc(ndoms * sizeof(cpumask_t), GFP_KERNEL);
-        if (!doms)
-                goto rebuild;
+        if (!doms) {
+                ndoms = 0;
+                goto done;
+        }
+
+        /*
+         * The rest of the code, including the scheduler, can deal with
+         * dattr==NULL case. No need to abort if alloc fails.
+         */
         dattr = kmalloc(ndoms * sizeof(struct sched_domain_attr), GFP_KERNEL);
 
         for (nslot = 0, i = 0; i < csn; i++) {
                 struct cpuset *a = csa[i];
+                cpumask_t *dp;
                 int apn = a->pn;
 
-                if (apn >= 0) {
-                        cpumask_t *dp = doms + nslot;
-
-                        if (nslot == ndoms) {
-                                static int warnings = 10;
-                                if (warnings) {
-                                        printk(KERN_WARNING
-                                         "rebuild_sched_domains confused:"
-                                          " nslot %d, ndoms %d, csn %d, i %d,"
-                                          " apn %d\n",
-                                          nslot, ndoms, csn, i, apn);
-                                        warnings--;
-                                }
-                                continue;
+                if (apn < 0) {
+                        /* Skip completed partitions */
+                        continue;
+                }
+
+                dp = doms + nslot;
+
+                if (nslot == ndoms) {
+                        static int warnings = 10;
+                        if (warnings) {
+                                printk(KERN_WARNING
+                                 "rebuild_sched_domains confused:"
+                                  " nslot %d, ndoms %d, csn %d, i %d,"
+                                  " apn %d\n",
+                                  nslot, ndoms, csn, i, apn);
+                                warnings--;
                         }
+                        continue;
+                }
 
-                        cpus_clear(*dp);
-                        if (dattr)
-                                *(dattr + nslot) = SD_ATTR_INIT;
-                        for (j = i; j < csn; j++) {
-                                struct cpuset *b = csa[j];
-
-                                if (apn == b->pn) {
-                                        cpus_or(*dp, *dp, b->cpus_allowed);
-                                        b->pn = -1;
-                                        if (dattr)
-                                                update_domain_attr_tree(dattr
-                                                                   + nslot, b);
-                                }
+                cpus_clear(*dp);
+                if (dattr)
+                        *(dattr + nslot) = SD_ATTR_INIT;
+                for (j = i; j < csn; j++) {
+                        struct cpuset *b = csa[j];
+
+                        if (apn == b->pn) {
+                                cpus_or(*dp, *dp, b->cpus_allowed);
+                                if (dattr)
+                                        update_domain_attr_tree(dattr + nslot, b);
+
+                                /* Done with this partition */
+                                b->pn = -1;
                         }
-                        nslot++;
                 }
+                nslot++;
         }
         BUG_ON(nslot != ndoms);
 
-rebuild:
-        /* Have scheduler rebuild sched domains */
+done:
+        kfree(csa);
+
+        *domains    = doms;
+        *attributes = dattr;
+        return ndoms;
+}
+
+/*
+ * Rebuild scheduler domains.
+ *
+ * Call with neither cgroup_mutex held nor within get_online_cpus().
+ * Takes both cgroup_mutex and get_online_cpus().
+ *
+ * Cannot be directly called from cpuset code handling changes
+ * to the cpuset pseudo-filesystem, because it cannot be called
+ * from code that already holds cgroup_mutex.
+ */
+static void do_rebuild_sched_domains(struct work_struct *unused)
+{
+        struct sched_domain_attr *attr;
+        cpumask_t *doms;
+        int ndoms;
+
         get_online_cpus();
-        partition_sched_domains(ndoms, doms, dattr);
+
+        /* Generate domain masks and attrs */
+        cgroup_lock();
+        ndoms = generate_sched_domains(&doms, &attr);
+        cgroup_unlock();
+
+        /* Have scheduler rebuild the domains */
+        partition_sched_domains(ndoms, doms, attr);
+
         put_online_cpus();
+}
 
-done:
-        kfree(csa);
-        /* Don't kfree(doms) -- partition_sched_domains() does that. */
-        /* Don't kfree(dattr) -- partition_sched_domains() does that. */
+static DECLARE_WORK(rebuild_sched_domains_work, do_rebuild_sched_domains);
+
+/*
+ * Rebuild scheduler domains, asynchronously via workqueue.
+ *
+ * If the flag 'sched_load_balance' of any cpuset with non-empty
+ * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
+ * which has that flag enabled, or if any cpuset with a non-empty
+ * 'cpus' is removed, then call this routine to rebuild the
+ * scheduler's dynamic sched domains.
+ *
+ * The rebuild_sched_domains() and partition_sched_domains()
+ * routines must nest cgroup_lock() inside get_online_cpus(),
+ * but such cpuset changes as these must nest that locking the
+ * other way, holding cgroup_lock() for much of the code.
+ *
+ * So in order to avoid an ABBA deadlock, the cpuset code handling
+ * these user changes delegates the actual sched domain rebuilding
+ * to a separate workqueue thread, which ends up processing the
+ * above do_rebuild_sched_domains() function.
+ */
+static void async_rebuild_sched_domains(void)
+{
+        schedule_work(&rebuild_sched_domains_work);
+}
+
+/*
+ * Accomplishes the same scheduler domain rebuild as the above
+ * async_rebuild_sched_domains(), however it directly calls the
+ * rebuild routine synchronously rather than calling it via an
+ * asynchronous work thread.
+ *
+ * This can only be called from code that is not holding
+ * cgroup_mutex (not nested in a cgroup_lock() call.)
+ */
+void rebuild_sched_domains(void)
+{
+        do_rebuild_sched_domains(NULL);
 }
 
 /**
@@ -863,7 +932,7 @@ static int update_cpumask(struct cpuset *cs, const char *buf)
                 return retval;
 
         if (is_load_balanced)
-                rebuild_sched_domains();
+                async_rebuild_sched_domains();
         return 0;
 }
 
@@ -1090,7 +1159,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
         if (val != cs->relax_domain_level) {
                 cs->relax_domain_level = val;
                 if (!cpus_empty(cs->cpus_allowed) && is_sched_load_balance(cs))
-                        rebuild_sched_domains();
+                        async_rebuild_sched_domains();
         }
 
         return 0;
@@ -1131,7 +1200,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
         mutex_unlock(&callback_mutex);
 
         if (cpus_nonempty && balance_flag_changed)
-                rebuild_sched_domains();
+                async_rebuild_sched_domains();
 
         return 0;
 }
@@ -1492,6 +1561,9 @@ static u64 cpuset_read_u64(struct cgroup *cont, struct cftype *cft)
         default:
                 BUG();
         }
+
+        /* Unreachable but makes gcc happy */
+        return 0;
 }
 
 static s64 cpuset_read_s64(struct cgroup *cont, struct cftype *cft)
@@ -1504,6 +1576,9 @@ static s64 cpuset_read_s64(struct cgroup *cont, struct cftype *cft)
         default:
                 BUG();
         }
+
+        /* Unrechable but makes gcc happy */
+        return 0;
 }
 
 
@@ -1692,15 +1767,9 @@ static struct cgroup_subsys_state *cpuset_create(
 }
 
 /*
- * Locking note on the strange update_flag() call below:
- *
  * If the cpuset being removed has its flag 'sched_load_balance'
  * enabled, then simulate turning sched_load_balance off, which
- * will call rebuild_sched_domains().  The get_online_cpus()
- * call in rebuild_sched_domains() must not be made while holding
- * callback_mutex.  Elsewhere the kernel nests callback_mutex inside
- * get_online_cpus() calls.  So the reverse nesting would risk an
- * ABBA deadlock.
+ * will call async_rebuild_sched_domains().
  */
 
 static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
@@ -1719,7 +1788,7 @@ static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
 struct cgroup_subsys cpuset_subsys = {
         .name = "cpuset",
         .create = cpuset_create,
-        .destroy  = cpuset_destroy,
+        .destroy = cpuset_destroy,
         .can_attach = cpuset_can_attach,
         .attach = cpuset_attach,
         .populate = cpuset_populate,
@@ -1811,7 +1880,7 @@ static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
 }
 
 /*
- * If common_cpu_mem_hotplug_unplug(), below, unplugs any CPUs
+ * If CPU and/or memory hotplug handlers, below, unplug any CPUs
  * or memory nodes, we need to walk over the cpuset hierarchy,
  * removing that CPU or node from all cpusets.  If this removes the
  * last CPU or node from a cpuset, then move the tasks in the empty
@@ -1903,35 +1972,6 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
 }
 
 /*
- * The cpus_allowed and mems_allowed nodemasks in the top_cpuset track
- * cpu_online_map and node_states[N_HIGH_MEMORY].  Force the top cpuset to
- * track what's online after any CPU or memory node hotplug or unplug event.
- *
- * Since there are two callers of this routine, one for CPU hotplug
- * events and one for memory node hotplug events, we could have coded
- * two separate routines here.  We code it as a single common routine
- * in order to minimize text size.
- */
-
-static void common_cpu_mem_hotplug_unplug(int rebuild_sd)
-{
-        cgroup_lock();
-
-        top_cpuset.cpus_allowed = cpu_online_map;
-        top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
-        scan_for_empty_cpusets(&top_cpuset);
-
-        /*
-         * Scheduler destroys domains on hotplug events.
-         * Rebuild them based on the current settings.
-         */
-        if (rebuild_sd)
-                rebuild_sched_domains();
-
-        cgroup_unlock();
-}
-
-/*
  * The top_cpuset tracks what CPUs and Memory Nodes are online,
  * period.  This is necessary in order to make cpusets transparent
  * (of no affect) on systems that are actively using CPU hotplug
@@ -1939,40 +1979,52 @@ static void common_cpu_mem_hotplug_unplug(int rebuild_sd)
  *
  * This routine ensures that top_cpuset.cpus_allowed tracks
  * cpu_online_map on each CPU hotplug (cpuhp) event.
+ *
+ * Called within get_online_cpus().  Needs to call cgroup_lock()
+ * before calling generate_sched_domains().
  */
-
-static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
+static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
                                 unsigned long phase, void *unused_cpu)
 {
+        struct sched_domain_attr *attr;
+        cpumask_t *doms;
+        int ndoms;
+
         switch (phase) {
-        case CPU_UP_CANCELED:
-        case CPU_UP_CANCELED_FROZEN:
-        case CPU_DOWN_FAILED:
-        case CPU_DOWN_FAILED_FROZEN:
         case CPU_ONLINE:
         case CPU_ONLINE_FROZEN:
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
-                common_cpu_mem_hotplug_unplug(1);
                 break;
+
         default:
                 return NOTIFY_DONE;
         }
 
+        cgroup_lock();
+        top_cpuset.cpus_allowed = cpu_online_map;
+        scan_for_empty_cpusets(&top_cpuset);
+        ndoms = generate_sched_domains(&doms, &attr);
+        cgroup_unlock();
+
+        /* Have scheduler rebuild the domains */
+        partition_sched_domains(ndoms, doms, attr);
+
         return NOTIFY_OK;
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
 /*
  * Keep top_cpuset.mems_allowed tracking node_states[N_HIGH_MEMORY].
- * Call this routine anytime after you change
- * node_states[N_HIGH_MEMORY].
- * See also the previous routine cpuset_handle_cpuhp().
+ * Call this routine anytime after node_states[N_HIGH_MEMORY] changes.
+ * See also the previous routine cpuset_track_online_cpus().
  */
-
 void cpuset_track_online_nodes(void)
 {
-        common_cpu_mem_hotplug_unplug(0);
+        cgroup_lock();
+        top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
+        scan_for_empty_cpusets(&top_cpuset);
+        cgroup_unlock();
 }
 #endif
 
@@ -1987,7 +2039,7 @@ void __init cpuset_init_smp(void)
         top_cpuset.cpus_allowed = cpu_online_map;
         top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
 
-        hotcpu_notifier(cpuset_handle_cpuhp, 0);
+        hotcpu_notifier(cpuset_track_online_cpus, 0);
 }
 
 /**