From: Ran Xiaokai <[email protected]>
If system has some isolate cpus with "isolcpus=" parameter,
and user try to offline all the non-isolated CPUs, kernel will
first report a warning and then panic when taking the last
non-isolated CPU offline.
Kernel should not panic when user managing CPUs with this
meaningless behavior, so we add a check for this, which
prevent user taking the last non-isolated CPU offline.
[ 19.415123] WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408
[ 19.430451] Call trace:
[ 19.430792] build_sched_domains+0x120c/0x1408
[ 19.431334] partition_sched_domains_locked+0x234/0x880
[ 19.431878] rebuild_sched_domains_locked+0x37c/0x798
[ 19.432436] rebuild_sched_domains+0x30/0x58
[ 19.432902] cpuset_hotplug_workfn+0x2a8/0x930
[ 19.433383] process_scheduled_works+0x178/0x3e0
[ 19.433878] worker_thread+0x174/0x2f0
[ 19.435204] ---[ end trace 0000000000000000 ]---
[ 19.438650] Unable to handle kernel paging request at virtual address fffe80027ab37080
[ 19.456414] partition_sched_domains_locked+0x318/0x880
[ 19.456899] rebuild_sched_domains_locked+0x37c/0x798
[ 19.457361] rebuild_sched_domains+0x30/0x58
[ 19.457761] cpuset_hotplug_workfn+0x2a8/0x930
[ 19.458175] process_scheduled_works+0x178/0x3e0
[ 19.458599] worker_thread+0x174/0x2f0
[ 19.458948] kthread+0x10c/0x128
[ 19.459268] ret_from_fork+0x10/0x20
[ 19.459728] Code: 1a850042 b9441883 f862dae0 8b000021 (f945003b)
Signed-off-by: Ran Xiaokai <[email protected]>
Cc: Xuexin Jiang <[email protected]>
Cc: Yang Yang <[email protected]>
---
kernel/cpu.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..09ecc19d2999 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1502,6 +1502,7 @@ static long __cpu_down_maps_locked(void *arg)
static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
struct cpu_down_work work = { .cpu = cpu, .target = target, };
+ struct cpumask tmp_mask;
/*
* If the platform does not support hotplug, report it explicitly to
@@ -1512,11 +1513,16 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
if (cpu_hotplug_disabled)
return -EBUSY;
+ /*
+ * Ensure the last non-isolated CPU is not offlined.
+ */
+ cpumask_and(&tmp_mask, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
+
/*
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
*/
- cpu = cpumask_any_but(cpu_online_mask, cpu);
+ cpu = cpumask_any_but(&tmp_mask, cpu);
if (cpu >= nr_cpu_ids)
return -EBUSY;
return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
--
2.15.2
On Sat, Sep 16 2023 at 10:37, yang wrote:
> @@ -1502,6 +1502,7 @@ static long __cpu_down_maps_locked(void *arg)
> static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
> {
> struct cpu_down_work work = { .cpu = cpu, .target = target, };
> + struct cpumask tmp_mask;
Allocating a cpumask on stack is not really a good idea as it takes up
to 1K stack space.
> /*
> * If the platform does not support hotplug, report it explicitly to
> @@ -1512,11 +1513,16 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
> if (cpu_hotplug_disabled)
> return -EBUSY;
>
> + /*
> + * Ensure the last non-isolated CPU is not offlined.
> + */
> + cpumask_and(&tmp_mask, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
You can spare that excercise. See below.
> /*
> * Ensure that the control task does not run on the to be offlined
> * CPU to prevent a deadlock against cfs_b->period_timer.
> */
> - cpu = cpumask_any_but(cpu_online_mask, cpu);
> + cpu = cpumask_any_but(&tmp_mask, cpu);
Just open code it this way:
for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) {
if (cpu != work.cpu)
return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
}
return -EBUSY;
Hmm?
Thanks,
tglx
From: Ran Xiaokai <[email protected]>
If system has some isolate cpus with "isolcpus=" parameter,
and user try to offline all the non-isolated CPUs, kernel will
first report a warning and then panic when taking the last
non-isolated CPU offline.
When offline the last non-isolate cpu,
cpuset_hotplug_workfn()
rebuild_sched_domains_locked()
ndoms = generate_sched_domains(&doms, &attr);
cpumask_and(doms[0], top_cpuset.effective_cpus,
housekeeping_cpumask(HK_FLAG_DOMAIN));
As isolated cpus are excluded, "doms" passes to partition_sched_domains_locked()
will be an empty cpumask.
WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408
Call trace:
build_sched_domains+0x120c/0x1408
partition_sched_domains_locked+0x234/0x880
rebuild_sched_domains_locked+0x37c/0x798
rebuild_sched_domains+0x30/0x58
cpuset_hotplug_workfn+0x2a8/0x930
process_scheduled_works+0x178/0x3e0
worker_thread+0x174/0x2f0
---[ end trace 0000000000000000 ]---
Unable to handle kernel paging request at virtual address fffe80027ab37080
partition_sched_domains_locked+0x318/0x880
rebuild_sched_domains_locked+0x37c/0x798
rebuild_sched_domains+0x30/0x58
cpuset_hotplug_workfn+0x2a8/0x930
process_scheduled_works+0x178/0x3e0
worker_thread+0x174/0x2f0
kthread+0x10c/0x128
ret_from_fork+0x10/0x20
Code: 1a850042 b9441883 f862dae0 8b000021 (f945003b)
Kernel should not panic when user managing CPUs with this
meaningless behavior, so we add a check for this, which
prevent user taking the last non-isolated CPU offline.
Signed-off-by: Ran Xiaokai <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Cc: Yang Yang <[email protected]>
Cc: Xuexin Jiang <[email protected]>
---
kernel/cpu.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..94430ea8b4a5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1515,11 +1515,14 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
/*
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
+ * Also keep at least one housekeeping cpu onlined to avoid generating
+ * an empty sched_domain span.
*/
- cpu = cpumask_any_but(cpu_online_mask, cpu);
- if (cpu >= nr_cpu_ids)
- return -EBUSY;
- return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
+ for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) {
+ if (cpu != work.cpu)
+ return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
+ }
+ return -EBUSY;
}
static int cpu_down(unsigned int cpu, enum cpuhp_state target)
--
2.15.2