[git pull] scheduler fixes

Ingo Molnar
2008-09-08T20:07:26Z

Linus,

Please pull the latest sched-fixes-for-linus git tree from:

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

These are cpusets related cpu hotplug race fixes that have been tested
to fix crashes and behavioral regressions that were reported.

Thanks,

Ingo

------------------>
Max Krasnyansky (2):
sched, cpuset: rework sched domains and CPU hotplug handling (v4)
sched: arch_reinit_sched_domains() must destroy domains to force rebuild

include/linux/cpuset.h | 2 +-
kernel/cpuset.c | 312 ++++++++++++++++++++++++++++--------------------
kernel/sched.c | 19 ++-
3 files changed, 196 insertions(+), 137 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index e8f450c..2691926 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -160,7 +160,7 @@ static inline int current_cpuset_is_being_rebound(void)

static inline void rebuild_sched_domains(void)
{
- partition_sched_domains(0, NULL, NULL);
+ partition_sched_domains(1, NULL, NULL);
}

#endif /* !CONFIG_CPUSETS */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d5ab79c..f227bc1 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);
}

/**
diff --git a/kernel/sched.c b/kernel/sched.c
index 1a5f73c..cc1f81b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7696,24 +7696,27 @@ static int dattrs_equal(struct sched_domain_attr *cur, int idx_cur,
* and partition_sched_domains() will fallback to the single partition
* 'fallback_doms', it also forces the domains to be rebuilt.
*
+ * If doms_new==NULL it will be replaced with cpu_online_map.
+ * ndoms_new==0 is a special case for destroying existing domains.
+ * It will not create the default domain.
+ *
* Call with hotplug lock held
*/
void partition_sched_domains(int ndoms_new, cpumask_t *doms_new,
struct sched_domain_attr *dattr_new)
{
- int i, j;
+ int i, j, n;

mutex_lock(&sched_domains_mutex);

/* always unregister in case we don't destroy any domains */
unregister_sched_domain_sysctl();

- if (doms_new == NULL)
- ndoms_new = 0;
+ n = doms_new ? ndoms_new : 0;

/* Destroy deleted domains */
for (i = 0; i < ndoms_cur; i++) {
- for (j = 0; j < ndoms_new; j++) {
+ for (j = 0; j < n; j++) {
if (cpus_equal(doms_cur[i], doms_new[j])
&& dattrs_equal(dattr_cur, i, dattr_new, j))
goto match1;
@@ -7726,7 +7729,6 @@ match1:

if (doms_new == NULL) {
ndoms_cur = 0;
- ndoms_new = 1;
doms_new = &fallback_doms;
cpus_andnot(doms_new[0], cpu_online_map, cpu_isolated_map);
dattr_new = NULL;
@@ -7763,8 +7765,13 @@ match2:
int arch_reinit_sched_domains(void)
{
get_online_cpus();
+
+ /* Destroy domains first to force the rebuild */
+ partition_sched_domains(0, NULL, NULL);
+
rebuild_sched_domains();
put_online_cpus();
+
return 0;
}

@@ -7848,7 +7855,7 @@ static int update_sched_domains(struct notifier_block *nfb,
case CPU_ONLINE_FROZEN:
case CPU_DEAD:
case CPU_DEAD_FROZEN:
- partition_sched_domains(0, NULL, NULL);
+ partition_sched_domains(1, NULL, NULL);
return NOTIFY_OK;