[PATCH cgroup/for-6.20 v5 0/5] cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict

[PATCH cgroup/for-6.20 v5 0/5] cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict

[Waiman Long]

 v5:
  - Fix patch 4 doc change as reported by Michael.

 v4:
  - Add tags and fix patch 4 commit log

 v3:
  - Patch 2: Change the condition for calling reset_partition_data() to
    (new_prs <= 0).
  - Patch 4: Update commit log and code comment to clarify the change.
  - Add a new patch 5 to move the empty cpus/mems check to
    cpuset1_validate_change().

 v2:
  - Patch 1: additional comment
  - Patch 2: simplify the conditions for triggering call to
    compute_excpus().
  - Patch 3: update description of cpuset.cpus.exclusive in cgroup-v2.rst
    to reflect the new behavior and change the name of the new
    cpus_excl_conflict() parameter to xcpus_changed.
  - Patch 4: update description of cpuset.cpus.partition in cgroup-v2.rst
    to clarify what exclusive CPUs will be used when a partition is
    created.

This patch series is inspired by the cpuset patch sent by Sun Shaojie [1].
The idea is to avoid invalidating sibling partitions when there is a
cpuset.cpus conflict. However this patch series does it in a slightly
different way to make its behavior more consistent with other cpuset
properties.

The first 3 patches are just some cleanup and minor bug fixes on
issues found during the investigation process. The last one is
the major patch that changes the way cpuset.cpus is being handled
during the partition creation process. Instead of invalidating sibling
partitions when there is a conflict, it will strip out the conflicting
exclusive CPUs and assign the remaining non-conflicting exclusive
CPUs to the new partition unless there is no more CPU left which will
fail the partition creation process. It is similar to the idea that
cpuset.cpus.effective may only contain a subset of CPUs specified in
cpuset.cpus. So cpuset.cpus.exclusive.effective may contain only a
subset of cpuset.cpus when a partition is created without setting
cpuset.cpus.exclusive.

Even setting cpuset.cpus.exclusive instead of cpuset.cpus may not
guarantee all the requested CPUs can be granted if parent doesn't have
access to some of those exclusive CPUs. The difference is that conflicts
from siblings is not possible with cpuset.cpus.exclusive as long as it
can be set successfully without failure.

[1] https://lore.kernel.org/lkml/20251117015708.977585-1-sunshaojie@kylinos.cn/

Waiman Long (5):
  cgroup/cpuset: Streamline rm_siblings_excl_cpus()
  cgroup/cpuset: Consistently compute effective_xcpus in
    update_cpumasks_hier()
  cgroup/cpuset: Don't fail cpuset.cpus change in v2
  cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus
    conflict
  cgroup/cpuset: Move the v1 empty cpus/mems check to
    cpuset1_validate_change()

 Documentation/admin-guide/cgroup-v2.rst       |  41 +++--
 kernel/cgroup/cpuset-internal.h               |  12 ++
 kernel/cgroup/cpuset-v1.c                     |  33 ++++
 kernel/cgroup/cpuset.c                        | 163 ++++++------------
 .../selftests/cgroup/test_cpuset_prs.sh       |  29 +++-
 5 files changed, 151 insertions(+), 127 deletions(-)

-- 
2.52.0

[PATCH cgroup/for-6.20 v5 1/5] cgroup/cpuset: Streamline rm_siblings_excl_cpus()

[Waiman Long]

If exclusive_cpus is set, effective_xcpus must be a subset of
exclusive_cpus. Currently, rm_siblings_excl_cpus() checks both
exclusive_cpus and effective_xcpus consecutively. It is simpler
to check only exclusive_cpus if non-empty or just effective_xcpus
otherwise.

No functional change is expected.

Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong<chenridong@huawei.com>
---
 kernel/cgroup/cpuset.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 221da921b4f9..da2b3b51630e 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1355,23 +1355,29 @@ static int rm_siblings_excl_cpus(struct cpuset *parent, struct cpuset *cs,
 	int retval = 0;
 
 	if (cpumask_empty(excpus))
-		return retval;
+		return 0;
 
 	/*
-	 * Exclude exclusive CPUs from siblings
+	 * Remove exclusive CPUs from siblings
 	 */
 	rcu_read_lock();
 	cpuset_for_each_child(sibling, css, parent) {
+		struct cpumask *sibling_xcpus;
+
 		if (sibling == cs)
 			continue;
 
-		if (cpumask_intersects(excpus, sibling->exclusive_cpus)) {
-			cpumask_andnot(excpus, excpus, sibling->exclusive_cpus);
-			retval++;
-			continue;
-		}
-		if (cpumask_intersects(excpus, sibling->effective_xcpus)) {
-			cpumask_andnot(excpus, excpus, sibling->effective_xcpus);
+		/*
+		 * If exclusive_cpus is defined, effective_xcpus will always
+		 * be a subset. Otherwise, effective_xcpus will only be set
+		 * in a valid partition root.
+		 */
+		sibling_xcpus = cpumask_empty(sibling->exclusive_cpus)
+			      ? sibling->effective_xcpus
+			      : sibling->exclusive_cpus;
+
+		if (cpumask_intersects(excpus, sibling_xcpus)) {
+			cpumask_andnot(excpus, excpus, sibling_xcpus);
 			retval++;
 		}
 	}
-- 
2.52.0

[PATCH cgroup/for-6.20 v5 2/5] cgroup/cpuset: Consistently compute effective_xcpus in update_cpumasks_hier()

[Waiman Long]

Since commit f62a5d39368e ("cgroup/cpuset: Remove remote_partition_check()
& make update_cpumasks_hier() handle remote partition"), the
compute_effective_exclusive_cpumask() helper was extended to
strip exclusive CPUs from siblings when computing effective_xcpus
(cpuset.cpus.exclusive.effective). This helper was later renamed to
compute_excpus() in commit 86bbbd1f33ab ("cpuset: Refactor exclusive
CPU mask computation logic").

This helper is supposed to be used consistently to compute
effective_xcpus. However, there is an exception within the callback
critical section in update_cpumasks_hier() when exclusive_cpus of a
valid partition root is empty. This can cause effective_xcpus value to
differ depending on where exactly it is last computed. Fix this by using
compute_excpus() in this case to give a consistent result.

Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
---
 kernel/cgroup/cpuset.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index da2b3b51630e..894131f47f78 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2168,17 +2168,13 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		spin_lock_irq(&callback_lock);
 		cpumask_copy(cp->effective_cpus, tmp->new_cpus);
 		cp->partition_root_state = new_prs;
-		if (!cpumask_empty(cp->exclusive_cpus) && (cp != cs))
-			compute_excpus(cp, cp->effective_xcpus);
-
 		/*
-		 * Make sure effective_xcpus is properly set for a valid
-		 * partition root.
+		 * Need to compute effective_xcpus if either exclusive_cpus
+		 * is non-empty or it is a valid partition root.
 		 */
-		if ((new_prs > 0) && cpumask_empty(cp->exclusive_cpus))
-			cpumask_and(cp->effective_xcpus,
-				    cp->cpus_allowed, parent->effective_xcpus);
-		else if (new_prs < 0)
+		if ((new_prs > 0) || !cpumask_empty(cp->exclusive_cpus))
+			compute_excpus(cp, cp->effective_xcpus);
+		if (new_prs <= 0)
 			reset_partition_data(cp);
 		spin_unlock_irq(&callback_lock);
 
-- 
2.52.0

[PATCH cgroup/for-6.20 v5 3/5] cgroup/cpuset: Don't fail cpuset.cpus change in v2

[Waiman Long]

Commit fe8cd2736e75 ("cgroup/cpuset: Delay setting of CS_CPU_EXCLUSIVE
until valid partition") introduced a new check to disallow the setting
of a new cpuset.cpus.exclusive value that is a superset of a sibling's
cpuset.cpus value so that there will at least be one CPU left in the
sibling in case the cpuset becomes a valid partition root. This new
check does have the side effect of failing a cpuset.cpus change that
make it a subset of a sibling's cpuset.cpus.exclusive value.

With v2, users are supposed to be allowed to set whatever value they
want in cpuset.cpus without failure. To maintain this rule, the check
is now restricted to only when cpuset.cpus.exclusive is being changed
not when cpuset.cpus is changed.

The cgroup-v2.rst doc file is also updated to reflect this change.

Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
---
 Documentation/admin-guide/cgroup-v2.rst |  8 +++----
 kernel/cgroup/cpuset.c                  | 30 ++++++++++++-------------
 2 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 7f5b59d95fce..510df2461aff 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2561,10 +2561,10 @@ Cpuset Interface Files
 	Users can manually set it to a value that is different from
 	"cpuset.cpus".	One constraint in setting it is that the list of
 	CPUs must be exclusive with respect to "cpuset.cpus.exclusive"
-	of its sibling.  If "cpuset.cpus.exclusive" of a sibling cgroup
-	isn't set, its "cpuset.cpus" value, if set, cannot be a subset
-	of it to leave at least one CPU available when the exclusive
-	CPUs are taken away.
+	and "cpuset.cpus.exclusive.effective" of its siblings.	Another
+	constraint is that it cannot be a superset of "cpuset.cpus"
+	of its sibling in order to leave at least one CPU available to
+	that sibling when the exclusive CPUs are taken away.
 
 	For a parent cgroup, any one of its exclusive CPUs can only
 	be distributed to at most one of its child cgroups.  Having an
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 894131f47f78..4819ab429771 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -609,33 +609,31 @@ static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
 
 /**
  * cpus_excl_conflict - Check if two cpusets have exclusive CPU conflicts
- * @cs1: first cpuset to check
- * @cs2: second cpuset to check
+ * @trial:	the trial cpuset to be checked
+ * @sibling:	a sibling cpuset to be checked against
+ * @xcpus_changed: set if exclusive_cpus has been set
  *
  * Returns: true if CPU exclusivity conflict exists, false otherwise
  *
  * Conflict detection rules:
  * 1. If either cpuset is CPU exclusive, they must be mutually exclusive
  * 2. exclusive_cpus masks cannot intersect between cpusets
- * 3. The allowed CPUs of one cpuset cannot be a subset of another's exclusive CPUs
+ * 3. The allowed CPUs of a sibling cpuset cannot be a subset of the new exclusive CPUs
  */
-static inline bool cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
+static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset *sibling,
+				      bool xcpus_changed)
 {
 	/* If either cpuset is exclusive, check if they are mutually exclusive */
-	if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
-		return !cpusets_are_exclusive(cs1, cs2);
+	if (is_cpu_exclusive(trial) || is_cpu_exclusive(sibling))
+		return !cpusets_are_exclusive(trial, sibling);
 
 	/* Exclusive_cpus cannot intersect */
-	if (cpumask_intersects(cs1->exclusive_cpus, cs2->exclusive_cpus))
+	if (cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus))
 		return true;
 
-	/* The cpus_allowed of one cpuset cannot be a subset of another cpuset's exclusive_cpus */
-	if (!cpumask_empty(cs1->cpus_allowed) &&
-	    cpumask_subset(cs1->cpus_allowed, cs2->exclusive_cpus))
-		return true;
-
-	if (!cpumask_empty(cs2->cpus_allowed) &&
-	    cpumask_subset(cs2->cpus_allowed, cs1->exclusive_cpus))
+	/* The cpus_allowed of a sibling cpuset cannot be a subset of the new exclusive_cpus */
+	if (xcpus_changed && !cpumask_empty(sibling->cpus_allowed) &&
+	    cpumask_subset(sibling->cpus_allowed, trial->exclusive_cpus))
 		return true;
 
 	return false;
@@ -672,6 +670,7 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
 {
 	struct cgroup_subsys_state *css;
 	struct cpuset *c, *par;
+	bool xcpus_changed;
 	int ret = 0;
 
 	rcu_read_lock();
@@ -728,10 +727,11 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
 	 * overlap. exclusive_cpus cannot overlap with each other if set.
 	 */
 	ret = -EINVAL;
+	xcpus_changed = !cpumask_equal(cur->exclusive_cpus, trial->exclusive_cpus);
 	cpuset_for_each_child(c, css, par) {
 		if (c == cur)
 			continue;
-		if (cpus_excl_conflict(trial, c))
+		if (cpus_excl_conflict(trial, c, xcpus_changed))
 			goto out;
 		if (mems_excl_conflict(trial, c))
 			goto out;
-- 
2.52.0

[PATCH cgroup/for-6.20 v5 4/5] cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict

[Waiman Long]

Currently, when setting a cpuset's cpuset.cpus to a value that conflicts
with the cpuset.cpus/cpuset.cpus.exclusive of a sibling partition,
the sibling's partition state becomes invalid. This is overly harsh and
is probably not necessary.

The cpuset.cpus.exclusive control file, if set, will override the
cpuset.cpus of the same cpuset when creating a cpuset partition.
So cpuset.cpus has less priority than cpuset.cpus.exclusive in setting up
a partition.  However, it cannot override a conflicting cpuset.cpus file
in a sibling cpuset and the partition creation process will fail. This
is inconsistent.  That will also make using cpuset.cpus.exclusive less
valuable as a tool to set up cpuset partitions as the users have to
check if such a cpuset.cpus conflict exists or not.

Fix these problems by making sure that once a cpuset.cpus.exclusive
is set without failure, it will always be allowed to form a valid
partition as long as at least one CPU can be granted from its parent
irrespective of the state of the siblings' cpuset.cpus values. Of
course, setting cpuset.cpus.exclusive will fail if it conflicts with
the cpuset.cpus.exclusive or the cpuset.cpus.exclusive.effective value
of a sibling.

Partition can still be created by setting only cpuset.cpus without
setting cpuset.cpus.exclusive. However, any conflicting CPUs in sibling's
cpuset.cpus.exclusive.effective and cpuset.cpus.exclusive values will
be removed from its cpuset.cpus.exclusive.effective as long as there
is still one or more CPUs left and can be granted from its parent. This
CPU stripping is currently done in rm_siblings_excl_cpus().

The new code will now try its best to enable the creation of new
partitions with only cpuset.cpus set without invalidating existing ones.
However it is not guaranteed that all the CPUs requested in cpuset.cpus
will be used in the new partition even when all these CPUs can be
granted from the parent.

This is similar to the fact that cpuset.cpus.effective may not be
able to include all the CPUs requested in cpuset.cpus. In this case,
the parent may not able to grant all the exclusive CPUs requested in
cpuset.cpus to cpuset.cpus.exclusive.effective if some of them have
already been granted to other partitions earlier.

With the creation of multiple sibling partitions by setting
only cpuset.cpus, this does have the side effect that their exact
cpuset.cpus.exclusive.effective settings will depend on the order of
partition creation if there are conflicts. Due to the exclusive nature
of the CPUs in a partition, it is not easy to make it fair other than
the old behavior of invalidating all the conflicting partitions.

For example,
  # echo "0-2" > A1/cpuset.cpus
  # echo "root" > A1/cpuset.cpus.partition
  # cat A1/cpuset.cpus.partition
  root
  # cat A1/cpuset.cpus.exclusive.effective
  0-2
  # echo "2-4" > B1/cpuset.cpus
  # echo "root" > B1/cpuset.cpus.partition
  # cat B1/cpuset.cpus.partition
  root
  # cat B1/cpuset.cpus.exclusive.effective
  3-4
  # cat B1/cpuset.cpus.effective
  3-4

For users who want to be sure that they can get most of the CPUs they
want, cpuset.cpus.exclusive should be used instead if they can set
it successfully without failure. Setting cpuset.cpus.exclusive will
guarantee that sibling conflicts from then onward is no longer possible.

To make this change, we have to separate out the is_cpu_exclusive()
check in cpus_excl_conflict() into a cgroup v1 only
cpuset1_cpus_excl_conflict() helper. The cpus_allowed_validate_change()
helper is now no longer needed and can be removed.

Some existing tests in test_cpuset_prs.sh are updated and new ones are
added to reflect the new behavior. The cgroup-v2.rst doc file is also
updated the clarify what exclusive CPUs will be used when a partition
is created.

Reported-by: Sun Shaojie <sunshaojie@kylinos.cn>
Closes: https://lore.kernel.org/lkml/20251117015708.977585-1-sunshaojie@kylinos.cn/
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
---
 Documentation/admin-guide/cgroup-v2.rst       | 33 +++++---
 kernel/cgroup/cpuset-internal.h               |  3 +
 kernel/cgroup/cpuset-v1.c                     | 19 +++++
 kernel/cgroup/cpuset.c                        | 80 ++++++-------------
 .../selftests/cgroup/test_cpuset_prs.sh       | 26 ++++--
 5 files changed, 90 insertions(+), 71 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 510df2461aff..28613c0e1c90 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2584,9 +2584,9 @@ Cpuset Interface Files
 	of this file will always be a subset of its parent's
 	"cpuset.cpus.exclusive.effective" if its parent is not the root
 	cgroup.  It will also be a subset of "cpuset.cpus.exclusive"
-	if it is set.  If "cpuset.cpus.exclusive" is not set, it is
-	treated to have an implicit value of "cpuset.cpus" in the
-	formation of local partition.
+	if it is set.  This file should only be non-empty if either
+	"cpuset.cpus.exclusive" is set or when the current cpuset is
+	a valid partition root.
 
   cpuset.cpus.isolated
 	A read-only and root cgroup only multiple values file.
@@ -2618,13 +2618,22 @@ Cpuset Interface Files
 	There are two types of partitions - local and remote.  A local
 	partition is one whose parent cgroup is also a valid partition
 	root.  A remote partition is one whose parent cgroup is not a
-	valid partition root itself.  Writing to "cpuset.cpus.exclusive"
-	is optional for the creation of a local partition as its
-	"cpuset.cpus.exclusive" file will assume an implicit value that
-	is the same as "cpuset.cpus" if it is not set.	Writing the
-	proper "cpuset.cpus.exclusive" values down the cgroup hierarchy
-	before the target partition root is mandatory for the creation
-	of a remote partition.
+	valid partition root itself.
+
+	Writing to "cpuset.cpus.exclusive" is optional for the creation
+	of a local partition as its "cpuset.cpus.exclusive" file will
+	assume an implicit value that is the same as "cpuset.cpus" if it
+	is not set.  Writing the proper "cpuset.cpus.exclusive" values
+	down the cgroup hierarchy before the target partition root is
+	mandatory for the creation of a remote partition.
+
+	Not all the CPUs requested in "cpuset.cpus.exclusive" can be
+	used to form a new partition.  Only those that were present
+	in its parent's "cpuset.cpus.exclusive.effective" control
+	file can be used.  For partitions created without setting
+	"cpuset.cpus.exclusive", exclusive CPUs specified in sibling's
+	"cpuset.cpus.exclusive" or "cpuset.cpus.exclusive.effective"
+	also cannot be used.
 
 	Currently, a remote partition cannot be created under a local
 	partition.  All the ancestors of a remote partition root except
@@ -2632,6 +2641,10 @@ Cpuset Interface Files
 
 	The root cgroup is always a partition root and its state cannot
 	be changed.  All other non-root cgroups start out as "member".
+	Even though the "cpuset.cpus.exclusive*" and "cpuset.cpus"
+	control files are not present in the root cgroup, they are
+	implicitly the same as the "/sys/devices/system/cpu/possible"
+	sysfs file.
 
 	When set to "root", the current cgroup is the root of a new
 	partition or scheduling domain.  The set of exclusive CPUs is
diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index e718a4f54360..e8e2683cb067 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -312,6 +312,7 @@ void cpuset1_hotplug_update_tasks(struct cpuset *cs,
 			    struct cpumask *new_cpus, nodemask_t *new_mems,
 			    bool cpus_updated, bool mems_updated);
 int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial);
+bool cpuset1_cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2);
 void cpuset1_init(struct cpuset *cs);
 void cpuset1_online_css(struct cgroup_subsys_state *css);
 int cpuset1_generate_sched_domains(cpumask_var_t **domains,
@@ -326,6 +327,8 @@ static inline void cpuset1_hotplug_update_tasks(struct cpuset *cs,
 			    bool cpus_updated, bool mems_updated) {}
 static inline int cpuset1_validate_change(struct cpuset *cur,
 				struct cpuset *trial) { return 0; }
+static inline bool cpuset1_cpus_excl_conflict(struct cpuset *cs1,
+					struct cpuset *cs2) { return false; }
 static inline void cpuset1_init(struct cpuset *cs) {}
 static inline void cpuset1_online_css(struct cgroup_subsys_state *css) {}
 static inline int cpuset1_generate_sched_domains(cpumask_var_t **domains,
diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
index ecfea7800f0d..04124c38a774 100644
--- a/kernel/cgroup/cpuset-v1.c
+++ b/kernel/cgroup/cpuset-v1.c
@@ -373,6 +373,25 @@ int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial)
 	return ret;
 }
 
+/*
+ * cpuset1_cpus_excl_conflict() - Check if two cpusets have exclusive CPU conflicts
+ *                                to legacy (v1)
+ * @cs1: first cpuset to check
+ * @cs2: second cpuset to check
+ *
+ * Returns: true if CPU exclusivity conflict exists, false otherwise
+ *
+ * If either cpuset is CPU exclusive, their allowed CPUs cannot intersect.
+ */
+bool cpuset1_cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
+{
+	if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
+		return cpumask_intersects(cs1->cpus_allowed,
+					  cs2->cpus_allowed);
+
+	return false;
+}
+
 #ifdef CONFIG_PROC_PID_CPUSET
 /*
  * proc_cpuset_show()
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 4819ab429771..83fb83a86b4b 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -129,6 +129,17 @@ static bool force_sd_rebuild;
  *  For simplicity, a local partition can be created under a local or remote
  *  partition but a remote partition cannot have any partition root in its
  *  ancestor chain except the cgroup root.
+ *
+ *  A valid partition can be formed by setting exclusive_cpus or cpus_allowed
+ *  if exclusive_cpus is not set. In the case of partition with empty
+ *  exclusive_cpus, all the conflicting exclusive CPUs specified in the
+ *  following cpumasks of sibling cpusets will be removed from its
+ *  cpus_allowed in determining its effective_xcpus.
+ *  - effective_xcpus
+ *  - exclusive_cpus
+ *
+ *  The "cpuset.cpus.exclusive" control file should be used for setting up
+ *  partition if the users want to get as many CPUs as possible.
  */
 #define PRS_MEMBER		0
 #define PRS_ROOT		1
@@ -616,27 +627,25 @@ static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
  * Returns: true if CPU exclusivity conflict exists, false otherwise
  *
  * Conflict detection rules:
- * 1. If either cpuset is CPU exclusive, they must be mutually exclusive
- * 2. exclusive_cpus masks cannot intersect between cpusets
- * 3. The allowed CPUs of a sibling cpuset cannot be a subset of the new exclusive CPUs
+ *  o cgroup v1
+ *    See cpuset1_cpus_excl_conflict()
+ *  o cgroup v2
+ *    - The exclusive_cpus values cannot overlap.
+ *    - New exclusive_cpus cannot be a superset of a sibling's cpus_allowed.
  */
 static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset *sibling,
 				      bool xcpus_changed)
 {
-	/* If either cpuset is exclusive, check if they are mutually exclusive */
-	if (is_cpu_exclusive(trial) || is_cpu_exclusive(sibling))
-		return !cpusets_are_exclusive(trial, sibling);
-
-	/* Exclusive_cpus cannot intersect */
-	if (cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus))
-		return true;
+	if (!cpuset_v2())
+		return cpuset1_cpus_excl_conflict(trial, sibling);
 
 	/* The cpus_allowed of a sibling cpuset cannot be a subset of the new exclusive_cpus */
 	if (xcpus_changed && !cpumask_empty(sibling->cpus_allowed) &&
 	    cpumask_subset(sibling->cpus_allowed, trial->exclusive_cpus))
 		return true;
 
-	return false;
+	/* Exclusive_cpus cannot intersect */
+	return cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus);
 }
 
 static inline bool mems_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
@@ -2312,43 +2321,6 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
 	return PERR_NONE;
 }
 
-static int cpus_allowed_validate_change(struct cpuset *cs, struct cpuset *trialcs,
-					struct tmpmasks *tmp)
-{
-	int retval;
-	struct cpuset *parent = parent_cs(cs);
-
-	retval = validate_change(cs, trialcs);
-
-	if ((retval == -EINVAL) && cpuset_v2()) {
-		struct cgroup_subsys_state *css;
-		struct cpuset *cp;
-
-		/*
-		 * The -EINVAL error code indicates that partition sibling
-		 * CPU exclusivity rule has been violated. We still allow
-		 * the cpumask change to proceed while invalidating the
-		 * partition. However, any conflicting sibling partitions
-		 * have to be marked as invalid too.
-		 */
-		trialcs->prs_err = PERR_NOTEXCL;
-		rcu_read_lock();
-		cpuset_for_each_child(cp, css, parent) {
-			struct cpumask *xcpus = user_xcpus(trialcs);
-
-			if (is_partition_valid(cp) &&
-			    cpumask_intersects(xcpus, cp->effective_xcpus)) {
-				rcu_read_unlock();
-				update_parent_effective_cpumask(cp, partcmd_invalidate, NULL, tmp);
-				rcu_read_lock();
-			}
-		}
-		rcu_read_unlock();
-		retval = 0;
-	}
-	return retval;
-}
-
 /**
  * partition_cpus_change - Handle partition state changes due to CPU mask updates
  * @cs: The target cpuset being modified
@@ -2408,15 +2380,15 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
 		return 0;
 
-	if (alloc_tmpmasks(&tmp))
-		return -ENOMEM;
-
 	compute_trialcs_excpus(trialcs, cs);
 	trialcs->prs_err = PERR_NONE;
 
-	retval = cpus_allowed_validate_change(cs, trialcs, &tmp);
+	retval = validate_change(cs, trialcs);
 	if (retval < 0)
-		goto out_free;
+		return retval;
+
+	if (alloc_tmpmasks(&tmp))
+		return -ENOMEM;
 
 	/*
 	 * Check all the descendants in update_cpumasks_hier() if
@@ -2439,7 +2411,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	/* Update CS_SCHED_LOAD_BALANCE and/or sched_domains, if necessary */
 	if (cs->partition_root_state)
 		update_partition_sd_lb(cs, old_prs);
-out_free:
+
 	free_tmpmasks(&tmp);
 	return retval;
 }
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index a17256d9f88a..ff4540b0490e 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -269,7 +269,7 @@ TEST_MATRIX=(
 	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X3:P2    .      .     0 A1:0-2|A2:3|A3:3 A1:P0|A2:P2 3"
 	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X2-3  X2-3:P2   .     0 A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
 	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X2-3 X2-3:P2:C3 .     0 A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
-	" C0-3:S+ C1-3:S+ C2-3   C2-3     .      .      .      P2    0 A1:0-3|A2:1-3|A3:2-3|B1:2-3 A1:P0|A3:P0|B1:P-2"
+	" C0-3:S+ C1-3:S+ C2-3   C2-3     .      .      .      P2    0 A1:0-1|A2:1|A3:1|B1:2-3 A1:P0|A3:P0|B1:P2"
 	" C0-3:S+ C1-3:S+ C2-3   C4-5     .      .      .      P2    0 B1:4-5 B1:P2 4-5"
 	" C0-3:S+ C1-3:S+ C2-3    C4    X2-3   X2-3  X2-3:P2   P2    0 A3:2-3|B1:4 A3:P2|B1:P2 2-4"
 	" C0-3:S+ C1-3:S+ C2-3    C4    X2-3   X2-3 X2-3:P2:C1-3 P2  0 A3:2-3|B1:4 A3:P2|B1:P2 2-4"
@@ -318,7 +318,7 @@ TEST_MATRIX=(
 	# Invalid to valid local partition direct transition tests
 	" C1-3:S+:P2 X4:P2  .      .      .      .      .      .     0 A1:1-3|XA1:1-3|A2:1-3:XA2: A1:P2|A2:P-2 1-3"
 	" C1-3:S+:P2 X4:P2  .      .      .    X3:P2    .      .     0 A1:1-2|XA1:1-3|A2:3:XA2:3 A1:P2|A2:P2 1-3"
-	"  C0-3:P2   .      .    C4-6   C0-4     .      .      .     0 A1:0-4|B1:4-6 A1:P-2|B1:P0"
+	"  C0-3:P2   .      .    C4-6   C0-4     .      .      .     0 A1:0-4|B1:5-6 A1:P2|B1:P0"
 	"  C0-3:P2   .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
 
 	# Local partition invalidation tests
@@ -388,10 +388,10 @@ TEST_MATRIX=(
 	"  C0-1:S+  C1      .    C2-3     .      P2     .      .     0 A1:0-1|A2:1 A1:P0|A2:P-2"
 	"  C0-1:S+ C1:P2    .    C2-3     P1     .      .      .     0 A1:0|A2:1 A1:P1|A2:P2 0-1|1"
 
-	# A non-exclusive cpuset.cpus change will invalidate partition and its siblings
-	"  C0-1:P1   .      .    C2-3   C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P-1|B1:P0"
-	"  C0-1:P1   .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P-1|B1:P-1"
-	"   C0-1     .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P0|B1:P-1"
+	# A non-exclusive cpuset.cpus change will not invalidate its siblings partition.
+	"  C0-1:P1   .      .    C2-3   C0-2     .      .      .     0 A1:0-2|B1:3 A1:P1|B1:P0"
+	"  C0-1:P1   .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-1|XA1:0-1|B1:2-3 A1:P1|B1:P1"
+	"   C0-1     .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-1|B1:2-3 A1:P0|B1:P1"
 
 	# cpuset.cpus can overlap with sibling cpuset.cpus.exclusive but not subsumed by it
 	"   C0-3     .      .    C4-5     X5     .      .      .     0 A1:0-3|B1:4-5"
@@ -417,6 +417,14 @@ TEST_MATRIX=(
 	" CX1-4:S+ CX2-4:P2 .    C5-6      .     .      .   P1:C3-6  0 A1:1|A2:2-4|B1:5-6 \
 								       A1:P0|A2:P2:B1:P-1 2-4"
 
+	# When multiple partitions with conflicting cpuset.cpus are created, the
+	# latter created ones will only get what are left of the available exclusive
+	# CPUs.
+	"  C1-3:P1   .      .      .       .     .      .   C3-5:P1  0 A1:1-3|B1:4-5:XB1:4-5 A1:P1|B1:P1"
+
+	# cpuset.cpus can be set to a subset of sibling's cpuset.cpus.exclusive
+	" C1-3:X1-3  .      .    C4-5      .     .      .     C1-2   0 A1:1-3|B1:1-2"
+
 	#  old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
 	#  ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
 	# Failure cases:
@@ -427,7 +435,7 @@ TEST_MATRIX=(
 	# Changes to cpuset.cpus.exclusive that violate exclusivity rule is rejected
 	"   C0-3     .      .    C4-5   X0-3     .      .     X3-5   1 A1:0-3|B1:4-5"
 
-	# cpuset.cpus cannot be a subset of sibling cpuset.cpus.exclusive
+	# cpuset.cpus.exclusive cannot be set to a superset of sibling's cpuset.cpus
 	"   C0-3     .      .    C4-5   X3-5     .      .      .     1 A1:0-3|B1:4-5"
 )
 
@@ -477,6 +485,10 @@ REMOTE_TEST_MATRIX=(
 	      .      .   X1-2:P2  X4-5:P1  .     X1-7:P2 p1:3|c11:1-2|c12:4:c22:5-6 \
 							 p1:P0|p2:P1|c11:P2|c12:P1|c22:P2 \
 							 1-2,4-6|1-2,5-6"
+	# c12 whose cpuset.cpus CPUs are all granted to c11 will become invalid partition
+	" C1-5:P1:S+ .  C1-4:P1   C2-3     .       .  \
+	      .      .     .       P1      .       .     p1:5|c11:1-4|c12:5 \
+							 p1:P1|c11:P1|c12:P-1"
 )
 
 #
-- 
2.52.0

[PATCH cgroup/for-6.20 v5 5/5] cgroup/cpuset: Move the v1 empty cpus/mems check to cpuset1_validate_change()

[Waiman Long]

As stated in commit 1c09b195d37f ("cpuset: fix a regression in validating
config change"), it is not allowed to clear masks of a cpuset if
there're tasks in it. This is specific to v1 since empty "cpuset.cpus"
or "cpuset.mems" will cause the v2 cpuset to inherit the effective CPUs
or memory nodes from its parent. So it is OK to have empty cpus or mems
even if there are tasks in the cpuset.

Move this empty cpus/mems check in validate_change() to
cpuset1_validate_change() to allow more flexibility in setting
cpus or mems in v2. cpuset_is_populated() needs to be moved into
cpuset-internal.h as it is needed by the empty cpus/mems checking code.

Also add a test case to test_cpuset_prs.sh to verify that.

Reported-by: Chen Ridong <chenridong@huaweicloud.com>
Closes: https://lore.kernel.org/lkml/7a3ec392-2e86-4693-aa9f-1e668a668b9c@huaweicloud.com/
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Chen Ridong <chenridong@huawei.com>
---
 kernel/cgroup/cpuset-internal.h               |  9 ++++++++
 kernel/cgroup/cpuset-v1.c                     | 14 +++++++++++
 kernel/cgroup/cpuset.c                        | 23 -------------------
 .../selftests/cgroup/test_cpuset_prs.sh       |  3 +++
 4 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
index e8e2683cb067..fd7d19842ded 100644
--- a/kernel/cgroup/cpuset-internal.h
+++ b/kernel/cgroup/cpuset-internal.h
@@ -260,6 +260,15 @@ static inline int nr_cpusets(void)
 	return static_key_count(&cpusets_enabled_key.key) + 1;
 }
 
+static inline bool cpuset_is_populated(struct cpuset *cs)
+{
+	lockdep_assert_cpuset_lock_held();
+
+	/* Cpusets in the process of attaching should be considered as populated */
+	return cgroup_is_populated(cs->css.cgroup) ||
+		cs->attach_in_progress;
+}
+
 /**
  * cpuset_for_each_child - traverse online children of a cpuset
  * @child_cs: loop cursor pointing to the current child
diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
index 04124c38a774..7a23b9e8778f 100644
--- a/kernel/cgroup/cpuset-v1.c
+++ b/kernel/cgroup/cpuset-v1.c
@@ -368,6 +368,20 @@ int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial)
 	if (par && !is_cpuset_subset(trial, par))
 		goto out;
 
+	/*
+	 * Cpusets with tasks - existing or newly being attached - can't
+	 * be changed to have empty cpus_allowed or mems_allowed.
+	 */
+	ret = -ENOSPC;
+	if (cpuset_is_populated(cur)) {
+		if (!cpumask_empty(cur->cpus_allowed) &&
+		    cpumask_empty(trial->cpus_allowed))
+			goto out;
+		if (!nodes_empty(cur->mems_allowed) &&
+		    nodes_empty(trial->mems_allowed))
+			goto out;
+	}
+
 	ret = 0;
 out:
 	return ret;
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 83fb83a86b4b..a3dbca125588 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -370,15 +370,6 @@ static inline bool is_in_v2_mode(void)
 	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
 }
 
-static inline bool cpuset_is_populated(struct cpuset *cs)
-{
-	lockdep_assert_held(&cpuset_mutex);
-
-	/* Cpusets in the process of attaching should be considered as populated */
-	return cgroup_is_populated(cs->css.cgroup) ||
-		cs->attach_in_progress;
-}
-
 /**
  * partition_is_populated - check if partition has tasks
  * @cs: partition root to be checked
@@ -695,20 +686,6 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
 
 	par = parent_cs(cur);
 
-	/*
-	 * Cpusets with tasks - existing or newly being attached - can't
-	 * be changed to have empty cpus_allowed or mems_allowed.
-	 */
-	ret = -ENOSPC;
-	if (cpuset_is_populated(cur)) {
-		if (!cpumask_empty(cur->cpus_allowed) &&
-		    cpumask_empty(trial->cpus_allowed))
-			goto out;
-		if (!nodes_empty(cur->mems_allowed) &&
-		    nodes_empty(trial->mems_allowed))
-			goto out;
-	}
-
 	/*
 	 * We can't shrink if we won't have enough room for SCHED_DEADLINE
 	 * tasks. This check is not done when scheduling is disabled as the
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index ff4540b0490e..5dff3ad53867 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -425,6 +425,9 @@ TEST_MATRIX=(
 	# cpuset.cpus can be set to a subset of sibling's cpuset.cpus.exclusive
 	" C1-3:X1-3  .      .    C4-5      .     .      .     C1-2   0 A1:1-3|B1:1-2"
 
+	# cpuset.cpus can become empty with task in it as it inherits parent's effective CPUs
+	" C1-3:S+   C2      .      .       .    T:C     .      .     0 A1:1-3|A2:1-3"
+
 	#  old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
 	#  ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
 	# Failure cases:
-- 
2.52.0

Re: [PATCH cgroup/for-6.20 v5 0/5] cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict

[Tejun Heo]

> Waiman Long (5):
>   cgroup/cpuset: Streamline rm_siblings_excl_cpus()
>   cgroup/cpuset: Consistently compute effective_xcpus in
>     update_cpumasks_hier()
>   cgroup/cpuset: Don't fail cpuset.cpus change in v2
>   cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus
>     conflict
>   cgroup/cpuset: Move the v1 empty cpus/mems check to
>     cpuset1_validate_change()

Applied 1-5 to cgroup/for-6.20.

Thanks.

--
tejun