[PATCH-cgroup 0/5] cgroup/cpuset: Miscellaneous cpuset updates for 6.12

[PATCH-cgroup 0/5] cgroup/cpuset: Miscellaneous cpuset updates for 6.12

[Waiman Long]

The first 2 patches in this series fix cpuset bugs found by Chen Ridong.
Patch 3 streamlines the sched domain rebuild process for hotplug
operation and eliminates the use of intermediate cpuset states for
sched domain generation. Patch 4 modifies generate_sched_domains()
to check the correctness of partition roots with non-overlapping CPUs.
Patch 5 adds new test cases to cover the bugs fixed in patches 1 and 2.

Chen Ridong (1):
  cgroup/cpuset: fix panic caused by partcmd_update

Waiman Long (4):
  cgroup/cpuset: Clear effective_xcpus on cpus_allowed clearing only if
    cpus.exclusive not set
  cgroup/cpuset: Eliminate unncessary sched domains rebuilds in hotplug
  cgroup/cpuset: Check for partition roots with overlapping CPUs
  selftest/cgroup: Add new test cases to test_cpuset_prs.sh

 kernel/cgroup/cpuset.c                        | 70 ++++++++++---------
 .../selftests/cgroup/test_cpuset_prs.sh       | 12 +++-
 2 files changed, 49 insertions(+), 33 deletions(-)

-- 
2.43.5

[PATCH-cgroup 1/5] cgroup/cpuset: fix panic caused by partcmd_update

[Waiman Long]

From: Chen Ridong <chenridong@huawei.com>

We find a bug as below:
BUG: unable to handle page fault for address: 00000003
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 3 PID: 358 Comm: bash Tainted: G        W I        6.6.0-10893-g60d6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/4
RIP: 0010:partition_sched_domains_locked+0x483/0x600
Code: 01 48 85 d2 74 0d 48 83 05 29 3f f8 03 01 f3 48 0f bc c2 89 c0 48 9
RSP: 0018:ffffc90000fdbc58 EFLAGS: 00000202
RAX: 0000000100000003 RBX: ffff888100b3dfa0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000002fe80
RBP: ffff888100b3dfb0 R08: 0000000000000001 R09: 0000000000000000
R10: ffffc90000fdbcb0 R11: 0000000000000004 R12: 0000000000000002
R13: ffff888100a92b48 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f44a5425740(0000) GS:ffff888237d80000(0000) knlGS:0000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100030973 CR3: 000000010722c000 CR4: 00000000000006e0
Call Trace:
 <TASK>
 ? show_regs+0x8c/0xa0
 ? __die_body+0x23/0xa0
 ? __die+0x3a/0x50
 ? page_fault_oops+0x1d2/0x5c0
 ? partition_sched_domains_locked+0x483/0x600
 ? search_module_extables+0x2a/0xb0
 ? search_exception_tables+0x67/0x90
 ? kernelmode_fixup_or_oops+0x144/0x1b0
 ? __bad_area_nosemaphore+0x211/0x360
 ? up_read+0x3b/0x50
 ? bad_area_nosemaphore+0x1a/0x30
 ? exc_page_fault+0x890/0xd90
 ? __lock_acquire.constprop.0+0x24f/0x8d0
 ? __lock_acquire.constprop.0+0x24f/0x8d0
 ? asm_exc_page_fault+0x26/0x30
 ? partition_sched_domains_locked+0x483/0x600
 ? partition_sched_domains_locked+0xf0/0x600
 rebuild_sched_domains_locked+0x806/0xdc0
 update_partition_sd_lb+0x118/0x130
 cpuset_write_resmask+0xffc/0x1420
 cgroup_file_write+0xb2/0x290
 kernfs_fop_write_iter+0x194/0x290
 new_sync_write+0xeb/0x160
 vfs_write+0x16f/0x1d0
 ksys_write+0x81/0x180
 __x64_sys_write+0x21/0x30
 x64_sys_call+0x2f25/0x4630
 do_syscall_64+0x44/0xb0
 entry_SYSCALL_64_after_hwframe+0x78/0xe2
RIP: 0033:0x7f44a553c887

It can be reproduced with cammands:
cd /sys/fs/cgroup/
mkdir test
cd test/
echo +cpuset > ../cgroup.subtree_control
echo root > cpuset.cpus.partition
cat /sys/fs/cgroup/cpuset.cpus.effective
0-3
echo 0-3 > cpuset.cpus // taking away all cpus from root

This issue is caused by the incorrect rebuilding of scheduling domains.
In this scenario, test/cpuset.cpus.partition should be an invalid root
and should not trigger the rebuilding of scheduling domains. When calling
update_parent_effective_cpumask with partcmd_update, if newmask is not
null, it should recheck newmask whether there are cpus is available
for parect/cs that has tasks.

Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2")
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 9066f9b4af24..f1846a08e245 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1978,6 +1978,8 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 			part_error = PERR_CPUSEMPTY;
 			goto write_error;
 		}
+		/* Check newmask again, whether cpus are available for parent/cs */
+		nocpu |= tasks_nocpu_error(parent, cs, newmask);
 
 		/*
 		 * partcmd_update with newmask:
-- 
2.43.5

[PATCH-cgroup 2/5] cgroup/cpuset: Clear effective_xcpus on cpus_allowed clearing only if cpus.exclusive not set

[Waiman Long]

Commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for
v2") adds a user writable cpuset.cpus.exclusive file for setting
exclusive CPUs to be used for the creation of partitions. Since then
effective_xcpus depends on both the cpuset.cpus and cpuset.cpus.exclusive
setting. If cpuset.cpus.exclusive is set, effective_xcpus will depend
only on cpuset.cpus.exclusive.  When it is not set, effective_xcpus
will be set according to the cpuset.cpus value when the cpuset becomes
a valid partition root.

When cpuset.cpus is being cleared by the user, effective_xcpus should
only be cleared when cpuset.cpus.exclusive is not set. However, that
is not currently the case.

  # cd /sys/fs/cgroup/
  # mkdir test
  # echo +cpuset > cgroup.subtree_control
  # cd test
  # echo 3 > cpuset.cpus.exclusive
  # cat cpuset.cpus.exclusive.effective
  3
  # echo > cpuset.cpus
  # cat cpuset.cpus.exclusive.effective // was cleared

Fix it by clearing effective_xcpus only if cpuset.cpus.exclusive is
not set.

Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
Reported-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f1846a08e245..7287cecb27d1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2508,7 +2508,8 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 	 */
 	if (!*buf) {
 		cpumask_clear(trialcs->cpus_allowed);
-		cpumask_clear(trialcs->effective_xcpus);
+		if (cpumask_empty(trialcs->exclusive_cpus))
+			cpumask_clear(trialcs->effective_xcpus);
 	} else {
 		retval = cpulist_parse(buf, trialcs->cpus_allowed);
 		if (retval < 0)
-- 
2.43.5

Re: [PATCH-cgroup 2/5] cgroup/cpuset: Clear effective_xcpus on cpus_allowed clearing only if cpus.exclusive not set

[Tejun Heo]

On Sun, Aug 04, 2024 at 09:30:16PM -0400, Waiman Long wrote:
> Commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for
> v2") adds a user writable cpuset.cpus.exclusive file for setting
> exclusive CPUs to be used for the creation of partitions. Since then
> effective_xcpus depends on both the cpuset.cpus and cpuset.cpus.exclusive
> setting. If cpuset.cpus.exclusive is set, effective_xcpus will depend
> only on cpuset.cpus.exclusive.  When it is not set, effective_xcpus
> will be set according to the cpuset.cpus value when the cpuset becomes
> a valid partition root.
> 
> When cpuset.cpus is being cleared by the user, effective_xcpus should
> only be cleared when cpuset.cpus.exclusive is not set. However, that
> is not currently the case.
> 
>   # cd /sys/fs/cgroup/
>   # mkdir test
>   # echo +cpuset > cgroup.subtree_control
>   # cd test
>   # echo 3 > cpuset.cpus.exclusive
>   # cat cpuset.cpus.exclusive.effective
>   3
>   # echo > cpuset.cpus
>   # cat cpuset.cpus.exclusive.effective // was cleared
> 
> Fix it by clearing effective_xcpus only if cpuset.cpus.exclusive is
> not set.
> 
> Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
> Reported-by: Chen Ridong <chenridong@huawei.com>
> Signed-off-by: Waiman Long <longman@redhat.com>

Applied 1-2 to cgroup/for-6.11-fixes w/ stable cc'd.

Thanks.

-- 
tejun

[PATCH-cgroup 3/5] cgroup/cpuset: Eliminate unncessary sched domains rebuilds in hotplug

[Waiman Long]

It was found that some hotplug operations may cause multiple
rebuild_sched_domains_locked() calls. Some of those intermediate calls
may use cpuset states not in the final correct form leading to incorrect
sched domain setting.

Fix this problem by using the existing force_rebuild flag to inhibit
immediate rebuild_sched_domains_locked() calls if set and only doing
one final call at the end. Also renaming the force_rebuild flag to
force_sd_rebuild to make its meaning for clear.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7287cecb27d1..e070e391d7a8 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -231,6 +231,13 @@ static cpumask_var_t	isolated_cpus;
 /* List of remote partition root children */
 static struct list_head remote_children;
 
+/*
+ * A flag to force sched domain rebuild at the end of an operation while
+ * inhibiting it in the intermediate stages when set. Currently it is only
+ * set in hotplug code.
+ */
+static bool force_sd_rebuild;
+
 /*
  * Partition root states:
  *
@@ -1467,7 +1474,7 @@ static void update_partition_sd_lb(struct cpuset *cs, int old_prs)
 			clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
 	}
 
-	if (rebuild_domains)
+	if (rebuild_domains && !force_sd_rebuild)
 		rebuild_sched_domains_locked();
 }
 
@@ -1820,7 +1827,7 @@ static void remote_partition_check(struct cpuset *cs, struct cpumask *newmask,
 			remote_partition_disable(child, tmp);
 			disable_cnt++;
 		}
-	if (disable_cnt)
+	if (disable_cnt && !force_sd_rebuild)
 		rebuild_sched_domains_locked();
 }
 
@@ -2425,7 +2432,8 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 	}
 	rcu_read_unlock();
 
-	if (need_rebuild_sched_domains && !(flags & HIER_NO_SD_REBUILD))
+	if (need_rebuild_sched_domains && !(flags & HIER_NO_SD_REBUILD) &&
+	    !force_sd_rebuild)
 		rebuild_sched_domains_locked();
 }
 
@@ -3087,7 +3095,8 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
 	cs->flags = trialcs->flags;
 	spin_unlock_irq(&callback_lock);
 
-	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
+	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed &&
+	    !force_sd_rebuild)
 		rebuild_sched_domains_locked();
 
 	if (spread_flag_changed)
@@ -4468,11 +4477,9 @@ hotplug_update_tasks(struct cpuset *cs,
 		update_tasks_nodemask(cs);
 }
 
-static bool force_rebuild;
-
 void cpuset_force_rebuild(void)
 {
-	force_rebuild = true;
+	force_sd_rebuild = true;
 }
 
 /**
@@ -4620,15 +4627,9 @@ static void cpuset_handle_hotplug(void)
 		       !cpumask_empty(subpartitions_cpus);
 	mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);
 
-	/*
-	 * In the rare case that hotplug removes all the cpus in
-	 * subpartitions_cpus, we assumed that cpus are updated.
-	 */
-	if (!cpus_updated && !cpumask_empty(subpartitions_cpus))
-		cpus_updated = true;
-
 	/* For v1, synchronize cpus_allowed to cpu_active_mask */
 	if (cpus_updated) {
+		cpuset_force_rebuild();
 		spin_lock_irq(&callback_lock);
 		if (!on_dfl)
 			cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
@@ -4684,8 +4685,8 @@ static void cpuset_handle_hotplug(void)
 	}
 
 	/* rebuild sched domains if cpus_allowed has changed */
-	if (cpus_updated || force_rebuild) {
-		force_rebuild = false;
+	if (force_sd_rebuild) {
+		force_sd_rebuild = false;
 		rebuild_sched_domains_cpuslocked();
 	}
 
-- 
2.43.5

Re: [PATCH-cgroup 3/5] cgroup/cpuset: Eliminate unncessary sched domains rebuilds in hotplug

[Tejun Heo]

On Sun, Aug 04, 2024 at 09:30:17PM -0400, Waiman Long wrote:
> It was found that some hotplug operations may cause multiple
> rebuild_sched_domains_locked() calls. Some of those intermediate calls
> may use cpuset states not in the final correct form leading to incorrect
> sched domain setting.
> 
> Fix this problem by using the existing force_rebuild flag to inhibit
> immediate rebuild_sched_domains_locked() calls if set and only doing
> one final call at the end. Also renaming the force_rebuild flag to
> force_sd_rebuild to make its meaning for clear.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>

Applied to cgroup/for-6.11-fixes.

Thanks.

-- 
tejun

[PATCH-cgroup 4/5] cgroup/cpuset: Check for partition roots with overlapping CPUs

[Waiman Long]

With the previous commit that eliminates the overlapping partition
root corner cases in the hotplug code, the partition roots passed down
to generate_sched_domains() should not have overlapping CPUs. Enable
overlapping cpuset check for v2 and warn if that happens.

This patch also has the benefit of increasing test coverage of the new
Union-Find cpuset merging code to cgroup v2.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e070e391d7a8..e34fd6108b06 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1127,25 +1127,27 @@ static int generate_sched_domains(cpumask_var_t **domains,
 	if (root_load_balance && (csn == 1))
 		goto single_root_domain;
 
-	if (!cgrpv2) {
-		for (i = 0; i < csn; i++)
-			uf_node_init(&csa[i]->node);
-
-		/* Merge overlapping cpusets */
-		for (i = 0; i < csn; i++) {
-			for (j = i + 1; j < csn; j++) {
-				if (cpusets_overlap(csa[i], csa[j]))
-					uf_union(&csa[i]->node, &csa[j]->node);
+	for (i = 0; i < csn; i++)
+		uf_node_init(&csa[i]->node);
+
+	/* Merge overlapping cpusets */
+	for (i = 0; i < csn; i++) {
+		for (j = i + 1; j < csn; j++) {
+			if (cpusets_overlap(csa[i], csa[j])) {
+				/*
+				 * Cgroup v2 shouldn't pass down overlapping
+				 * partition root cpusets.
+				 */
+				WARN_ON_ONCE(cgrpv2);
+				uf_union(&csa[i]->node, &csa[j]->node);
 			}
 		}
+	}
 
-		/* Count the total number of domains */
-		for (i = 0; i < csn; i++) {
-			if (uf_find(&csa[i]->node) == &csa[i]->node)
-				ndoms++;
-		}
-	} else {
-		ndoms = csn;
+	/* Count the total number of domains */
+	for (i = 0; i < csn; i++) {
+		if (uf_find(&csa[i]->node) == &csa[i]->node)
+			ndoms++;
 	}
 
 	/*
-- 
2.43.5

[PATCH-cgroup 5/5] selftest/cgroup: Add new test cases to test_cpuset_prs.sh

[Waiman Long]

Add new test cases to test_cpuset_prs.sh to cover corner cases reported
in previous fix commits.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index 7c08cc153367..7295424502b9 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -321,7 +321,7 @@ TEST_MATRIX=(
 	#  old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
 	#  ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
 	#
-	# Incorrect change to cpuset.cpus invalidates partition root
+	# Incorrect change to cpuset.cpus[.exclusive] invalidates partition root
 	#
 	# Adding CPUs to partition root that are not in parent's
 	# cpuset.cpus is allowed, but those extra CPUs are ignored.
@@ -365,6 +365,16 @@ TEST_MATRIX=(
 	# 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"
 
+	# Child partition root that try to take all CPUs from parent partition
+	# with tasks will remain invalid.
+	" C1-4:P1:S+ P1     .      .       .     .      .      .     0 A1:1-4,A2:1-4 A1:P1,A2:P-1"
+	" C1-4:P1:S+ P1     .      .       .   C1-4     .      .     0 A1,A2:1-4 A1:P1,A2:P1"
+	" C1-4:P1:S+ P1     .      .       T   C1-4     .      .     0 A1:1-4,A2:1-4 A1:P1,A2:P-1"
+
+	# Clearing of cpuset.cpus with a preset cpuset.cpus.exclusive shouldn't
+	# affect cpuset.cpus.exclusive.effective.
+	" C1-4:X3:S+ C1:X3  .      .       .     C      .      .     0 A2:1-4,XA2:3"
+
 	#  old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
 	#  ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
 	# Failure cases:
-- 
2.43.5

Re: [PATCH-cgroup 5/5] selftest/cgroup: Add new test cases to test_cpuset_prs.sh

[Tejun Heo]

On Sun, Aug 04, 2024 at 09:30:19PM -0400, Waiman Long wrote:
> Add new test cases to test_cpuset_prs.sh to cover corner cases reported
> in previous fix commits.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>

Applied 4-5 to cgroup/for-6.12 after pulling in cgroup/for-6.11-fixes.

Thanks.

-- 
tejun