* [PATCH 0/2] sched: Address idle task vs pcpu kthread checks
@ 2021-05-10 15:10 Valentin Schneider
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
` (2 more replies)
0 siblings, 3 replies; 13+ messages in thread
From: Valentin Schneider @ 2021-05-10 15:10 UTC (permalink / raw)
To: linux-kernel; +Cc: mingo, peterz, tglx, bristot, yejune.deng
Commit
5ba2ffba13a1 ("sched: Fix CPU hotplug / tighten is_per_cpu_kthread()")
had to special-case the idle task when checking for per-CPU kthreads. This is
due to the idle task not having its own struct kthread, which is where we'd
store KTHREAD_IS_PER_CPU.
From staring at Yejune's recent patch [1], it turns out the idle task is also
missing PF_NO_SETAFFINITY.
Patch 1 cleans this up, patch 2 is Yejune's v1 which depends on it.
Note: I remember seeing some patch(es) from Peter tackling this exact
problem, but I couldn't find them again.
[1]: http://lore.kernel.org/r/1620458722-13026-1-git-send-email-yejunedeng@gmail.com
Cheers,
Valentin
Valentin Schneider (1):
sched: Make the idle task quack like a per-CPU kthread
Yejune Deng (1):
lib/smp_processor_id: Use is_percpu_thread() instead of
nr_cpus_allowed
include/linux/kthread.h | 2 ++
kernel/kthread.c | 30 ++++++++++++++++++------------
kernel/sched/core.c | 21 +++++++++++++++------
lib/smp_processor_id.c | 6 +-----
4 files changed, 36 insertions(+), 23 deletions(-)
--
2.25.1
^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread
2021-05-10 15:10 [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Valentin Schneider
@ 2021-05-10 15:10 ` Valentin Schneider
2021-05-10 15:57 ` Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
2021-05-12 11:00 ` [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Peter Zijlstra
2 siblings, 2 replies; 13+ messages in thread
From: Valentin Schneider @ 2021-05-10 15:10 UTC (permalink / raw)
To: linux-kernel; +Cc: mingo, peterz, tglx, bristot, yejune.deng
For all intents and purposes, the idle task is a per-CPU kthread. It isn't
created via the same route as other pcpu kthreads however, and as a result
it is missing a few bells and whistles: it fails kthread_is_per_cpu() and
it doesn't have PF_NO_SETAFFINITY set.
Fix the former by giving the idle task a kthread struct along with the
KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle()
call be called more than once on the same idle task.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
include/linux/kthread.h | 2 ++
kernel/kthread.c | 30 ++++++++++++++++++------------
kernel/sched/core.c | 21 +++++++++++++++------
3 files changed, 35 insertions(+), 18 deletions(-)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 2484ed97e72f..d9133d6db308 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -33,6 +33,8 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
unsigned int cpu,
const char *namefmt);
+void set_kthread_struct(struct task_struct *p);
+
void kthread_set_per_cpu(struct task_struct *k, int cpu);
bool kthread_is_per_cpu(struct task_struct *k);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 6d3c488a0f82..77dd0ea1d35d 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -68,16 +68,6 @@ enum KTHREAD_BITS {
KTHREAD_SHOULD_PARK,
};
-static inline void set_kthread_struct(void *kthread)
-{
- /*
- * We abuse ->set_child_tid to avoid the new member and because it
- * can't be wrongly copied by copy_process(). We also rely on fact
- * that the caller can't exec, so PF_KTHREAD can't be cleared.
- */
- current->set_child_tid = (__force void __user *)kthread;
-}
-
static inline struct kthread *to_kthread(struct task_struct *k)
{
WARN_ON(!(k->flags & PF_KTHREAD));
@@ -103,6 +93,22 @@ static inline struct kthread *__to_kthread(struct task_struct *p)
return kthread;
}
+void set_kthread_struct(struct task_struct *p)
+{
+ struct kthread *kthread;
+
+ if (__to_kthread(p))
+ return;
+
+ kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
+ /*
+ * We abuse ->set_child_tid to avoid the new member and because it
+ * can't be wrongly copied by copy_process(). We also rely on fact
+ * that the caller can't exec, so PF_KTHREAD can't be cleared.
+ */
+ p->set_child_tid = (__force void __user *)kthread;
+}
+
void free_kthread_struct(struct task_struct *k)
{
struct kthread *kthread;
@@ -272,8 +278,8 @@ static int kthread(void *_create)
struct kthread *self;
int ret;
- self = kzalloc(sizeof(*self), GFP_KERNEL);
- set_kthread_struct(self);
+ set_kthread_struct(current);
+ self = to_kthread(current);
/* If user was SIGKILLed, I release the structure. */
done = xchg(&create->done, NULL);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4a0668acd876..5bb720829d93 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7440,12 +7440,25 @@ void init_idle(struct task_struct *idle, int cpu)
__sched_fork(0, idle);
+ /*
+ * The idle task doesn't need the kthread struct to function, but it
+ * is dressed up as a per-CPU kthread and thus needs to play the part
+ * if we want to avoid special-casing it in code that deals with per-CPU
+ * kthreads.
+ */
+ set_kthread_struct(idle);
+
raw_spin_lock_irqsave(&idle->pi_lock, flags);
raw_spin_lock(&rq->lock);
idle->state = TASK_RUNNING;
idle->se.exec_start = sched_clock();
- idle->flags |= PF_IDLE;
+ /*
+ * PF_KTHREAD should already be set at this point; regardless, make it
+ * look like a proper per-CPU kthread.
+ */
+ idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY;
+ kthread_set_per_cpu(idle, cpu);
scs_task_reset(idle);
kasan_unpoison_task_stack(idle);
@@ -7662,12 +7675,8 @@ static void balance_push(struct rq *rq)
/*
* Both the cpu-hotplug and stop task are in this case and are
* required to complete the hotplug process.
- *
- * XXX: the idle task does not match kthread_is_per_cpu() due to
- * histerical raisins.
*/
- if (rq->idle == push_task ||
- kthread_is_per_cpu(push_task) ||
+ if (kthread_is_per_cpu(push_task) ||
is_migration_disabled(push_task)) {
/*
--
2.25.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
2021-05-10 15:10 [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Valentin Schneider
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
@ 2021-05-10 15:10 ` Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Yejune Deng
2021-05-19 9:02 ` tip-bot2 for Yejune Deng
2021-05-12 11:00 ` [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Peter Zijlstra
2 siblings, 2 replies; 13+ messages in thread
From: Valentin Schneider @ 2021-05-10 15:10 UTC (permalink / raw)
To: linux-kernel; +Cc: Yejune Deng, mingo, peterz, tglx, bristot
From: Yejune Deng <yejune.deng@gmail.com>
is_percpu_thread() more elegantly handles SMP vs UP, and further checks the
presence of PF_NO_SETAFFINITY. This lets us catch cases where
check_preemption_disabled() can race with a concurrent sched_setaffinity().
Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
[Amended changelog]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
lib/smp_processor_id.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 1c1dbd300325..046ac6297c78 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
if (irqs_disabled())
goto out;
- /*
- * Kernel threads bound to a single CPU can safely use
- * smp_processor_id():
- */
- if (current->nr_cpus_allowed == 1)
+ if (is_percpu_thread())
goto out;
#ifdef CONFIG_SMP
--
2.25.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
@ 2021-05-10 15:57 ` Valentin Schneider
2021-05-11 7:32 ` Ingo Molnar
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
1 sibling, 1 reply; 13+ messages in thread
From: Valentin Schneider @ 2021-05-10 15:57 UTC (permalink / raw)
To: linux-kernel; +Cc: mingo, peterz, tglx, bristot, yejune.deng
On 10/05/21 16:10, Valentin Schneider wrote:
> This requires some extra iffery as init_idle()
> call be called more than once on the same idle task.
>
While I'm at it, do we actually still need to suffer through this?
AFAICT the extra calls are due to idle_thread_get() (used in cpuhp) calling
init_idle(). However it looks to me that since
3bb5d2ee396a ("smp, idle: Allocate idle thread for each possible cpu during boot")
we don't need to do that: we already have a
for_each_possible_cpu(cpu)
init_idle(cpu)
issued at init. So can't we "simply" rely on that init-time creation, given
it's done against the possible mask? I think the only thing that might need
doing at later hotplug is making sure the preempt count is right (secondary
startups seem to all prepare the idle task by issuing a preempt_disable()).
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread
2021-05-10 15:57 ` Valentin Schneider
@ 2021-05-11 7:32 ` Ingo Molnar
2021-05-11 9:33 ` Valentin Schneider
0 siblings, 1 reply; 13+ messages in thread
From: Ingo Molnar @ 2021-05-11 7:32 UTC (permalink / raw)
To: Valentin Schneider; +Cc: linux-kernel, peterz, tglx, bristot, yejune.deng
* Valentin Schneider <valentin.schneider@arm.com> wrote:
> On 10/05/21 16:10, Valentin Schneider wrote:
> > This requires some extra iffery as init_idle()
> > call be called more than once on the same idle task.
> >
>
> While I'm at it, do we actually still need to suffer through this?
No.
> AFAICT the extra calls are due to idle_thread_get() (used in cpuhp)
> calling init_idle(). However it looks to me that since
>
> 3bb5d2ee396a ("smp, idle: Allocate idle thread for each possible cpu during boot")
>
> we don't need to do that: we already have a
>
> for_each_possible_cpu(cpu)
> init_idle(cpu)
>
> issued at init. So can't we "simply" rely on that init-time creation,
> given it's done against the possible mask? I think the only thing that
> might need doing at later hotplug is making sure the preempt count is
> right (secondary startups seem to all prepare the idle task by issuing a
> preempt_disable()).
Best-case it works, worst-case we discover an unclean assumption in the
init sequence and it works after we fix that.
Win-win. :-)
Thanks,
Ingo
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread
2021-05-11 7:32 ` Ingo Molnar
@ 2021-05-11 9:33 ` Valentin Schneider
0 siblings, 0 replies; 13+ messages in thread
From: Valentin Schneider @ 2021-05-11 9:33 UTC (permalink / raw)
To: Ingo Molnar; +Cc: linux-kernel, peterz, tglx, bristot, yejune.deng
On 11/05/21 09:32, Ingo Molnar wrote:
> * Valentin Schneider <valentin.schneider@arm.com> wrote:
>> AFAICT the extra calls are due to idle_thread_get() (used in cpuhp)
>> calling init_idle(). However it looks to me that since
>>
>> 3bb5d2ee396a ("smp, idle: Allocate idle thread for each possible cpu during boot")
>>
>> we don't need to do that: we already have a
>>
>> for_each_possible_cpu(cpu)
>> init_idle(cpu)
>>
>> issued at init. So can't we "simply" rely on that init-time creation,
>> given it's done against the possible mask? I think the only thing that
>> might need doing at later hotplug is making sure the preempt count is
>> right (secondary startups seem to all prepare the idle task by issuing a
>> preempt_disable()).
>
> Best-case it works, worst-case we discover an unclean assumption in the
> init sequence and it works after we fix that.
>
> Win-win. :-)
>
Well I got something that seems to work, let me it test it some more and
convince myself it isn't completely bonkers and I'll toss it out.
> Thanks,
>
> Ingo
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH 0/2] sched: Address idle task vs pcpu kthread checks
2021-05-10 15:10 [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Valentin Schneider
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
@ 2021-05-12 11:00 ` Peter Zijlstra
2 siblings, 0 replies; 13+ messages in thread
From: Peter Zijlstra @ 2021-05-12 11:00 UTC (permalink / raw)
To: Valentin Schneider; +Cc: linux-kernel, mingo, tglx, bristot, yejune.deng
On Mon, May 10, 2021 at 04:10:22PM +0100, Valentin Schneider wrote:
> Note: I remember seeing some patch(es) from Peter tackling this exact
> problem, but I couldn't find them again.
Found it (by accident), yours is nicer though :-)
> Valentin Schneider (1):
> sched: Make the idle task quack like a per-CPU kthread
>
> Yejune Deng (1):
> lib/smp_processor_id: Use is_percpu_thread() instead of
> nr_cpus_allowed
>
> include/linux/kthread.h | 2 ++
> kernel/kthread.c | 30 ++++++++++++++++++------------
> kernel/sched/core.c | 21 +++++++++++++++------
> lib/smp_processor_id.c | 6 +-----
> 4 files changed, 36 insertions(+), 23 deletions(-)
Thanks!
^ permalink raw reply [flat|nested] 13+ messages in thread
* [tip: sched/core] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
@ 2021-05-19 8:09 ` tip-bot2 for Yejune Deng
2021-05-19 9:02 ` tip-bot2 for Yejune Deng
1 sibling, 0 replies; 13+ messages in thread
From: tip-bot2 for Yejune Deng @ 2021-05-19 8:09 UTC (permalink / raw)
To: linux-tip-commits
Cc: Valentin Schneider, Yejune Deng, Peter Zijlstra (Intel),
x86, linux-kernel
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 0019699518cc026b5bd912425be8e424843d5b33
Gitweb: https://git.kernel.org/tip/0019699518cc026b5bd912425be8e424843d5b33
Author: Yejune Deng <yejune.deng@gmail.com>
AuthorDate: Mon, 10 May 2021 16:10:24 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 18 May 2021 12:53:54 +02:00
lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
is_percpu_thread() more elegantly handles SMP vs UP, and further checks the
presence of PF_NO_SETAFFINITY. This lets us catch cases where
check_preemption_disabled() can race with a concurrent sched_setaffinity().
[Amended changelog]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@arm.com
---
lib/smp_processor_id.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 1c1dbd3..046ac62 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
if (irqs_disabled())
goto out;
- /*
- * Kernel threads bound to a single CPU can safely use
- * smp_processor_id():
- */
- if (current->nr_cpus_allowed == 1)
+ if (is_percpu_thread())
goto out;
#ifdef CONFIG_SMP
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [tip: sched/core] sched: Make the idle task quack like a per-CPU kthread
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
2021-05-10 15:57 ` Valentin Schneider
@ 2021-05-19 8:09 ` tip-bot2 for Valentin Schneider
1 sibling, 0 replies; 13+ messages in thread
From: tip-bot2 for Valentin Schneider @ 2021-05-19 8:09 UTC (permalink / raw)
To: linux-tip-commits
Cc: Valentin Schneider, Peter Zijlstra (Intel), x86, linux-kernel
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 00b89fe0197f0c55a045775c11553c0cdb7082fe
Gitweb: https://git.kernel.org/tip/00b89fe0197f0c55a045775c11553c0cdb7082fe
Author: Valentin Schneider <valentin.schneider@arm.com>
AuthorDate: Mon, 10 May 2021 16:10:23 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 18 May 2021 12:53:53 +02:00
sched: Make the idle task quack like a per-CPU kthread
For all intents and purposes, the idle task is a per-CPU kthread. It isn't
created via the same route as other pcpu kthreads however, and as a result
it is missing a few bells and whistles: it fails kthread_is_per_cpu() and
it doesn't have PF_NO_SETAFFINITY set.
Fix the former by giving the idle task a kthread struct along with the
KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle()
call be called more than once on the same idle task.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510151024.2448573-2-valentin.schneider@arm.com
---
include/linux/kthread.h | 2 ++
kernel/kthread.c | 30 ++++++++++++++++++------------
kernel/sched/core.c | 21 +++++++++++++++------
3 files changed, 35 insertions(+), 18 deletions(-)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 2484ed9..d9133d6 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -33,6 +33,8 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
unsigned int cpu,
const char *namefmt);
+void set_kthread_struct(struct task_struct *p);
+
void kthread_set_per_cpu(struct task_struct *k, int cpu);
bool kthread_is_per_cpu(struct task_struct *k);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index fe3f2a4..3d32683 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -68,16 +68,6 @@ enum KTHREAD_BITS {
KTHREAD_SHOULD_PARK,
};
-static inline void set_kthread_struct(void *kthread)
-{
- /*
- * We abuse ->set_child_tid to avoid the new member and because it
- * can't be wrongly copied by copy_process(). We also rely on fact
- * that the caller can't exec, so PF_KTHREAD can't be cleared.
- */
- current->set_child_tid = (__force void __user *)kthread;
-}
-
static inline struct kthread *to_kthread(struct task_struct *k)
{
WARN_ON(!(k->flags & PF_KTHREAD));
@@ -103,6 +93,22 @@ static inline struct kthread *__to_kthread(struct task_struct *p)
return kthread;
}
+void set_kthread_struct(struct task_struct *p)
+{
+ struct kthread *kthread;
+
+ if (__to_kthread(p))
+ return;
+
+ kthread = kzalloc(sizeof(*kthread), GFP_KERNEL);
+ /*
+ * We abuse ->set_child_tid to avoid the new member and because it
+ * can't be wrongly copied by copy_process(). We also rely on fact
+ * that the caller can't exec, so PF_KTHREAD can't be cleared.
+ */
+ p->set_child_tid = (__force void __user *)kthread;
+}
+
void free_kthread_struct(struct task_struct *k)
{
struct kthread *kthread;
@@ -272,8 +278,8 @@ static int kthread(void *_create)
struct kthread *self;
int ret;
- self = kzalloc(sizeof(*self), GFP_KERNEL);
- set_kthread_struct(self);
+ set_kthread_struct(current);
+ self = to_kthread(current);
/* If user was SIGKILLed, I release the structure. */
done = xchg(&create->done, NULL);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 24fd795..6a5124c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8234,12 +8234,25 @@ void __init init_idle(struct task_struct *idle, int cpu)
__sched_fork(0, idle);
+ /*
+ * The idle task doesn't need the kthread struct to function, but it
+ * is dressed up as a per-CPU kthread and thus needs to play the part
+ * if we want to avoid special-casing it in code that deals with per-CPU
+ * kthreads.
+ */
+ set_kthread_struct(idle);
+
raw_spin_lock_irqsave(&idle->pi_lock, flags);
raw_spin_rq_lock(rq);
idle->state = TASK_RUNNING;
idle->se.exec_start = sched_clock();
- idle->flags |= PF_IDLE;
+ /*
+ * PF_KTHREAD should already be set at this point; regardless, make it
+ * look like a proper per-CPU kthread.
+ */
+ idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY;
+ kthread_set_per_cpu(idle, cpu);
scs_task_reset(idle);
kasan_unpoison_task_stack(idle);
@@ -8456,12 +8469,8 @@ static void balance_push(struct rq *rq)
/*
* Both the cpu-hotplug and stop task are in this case and are
* required to complete the hotplug process.
- *
- * XXX: the idle task does not match kthread_is_per_cpu() due to
- * histerical raisins.
*/
- if (rq->idle == push_task ||
- kthread_is_per_cpu(push_task) ||
+ if (kthread_is_per_cpu(push_task) ||
is_migration_disabled(push_task)) {
/*
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [tip: sched/core] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Yejune Deng
@ 2021-05-19 9:02 ` tip-bot2 for Yejune Deng
2021-05-31 10:21 ` [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot Peter Zijlstra
1 sibling, 1 reply; 13+ messages in thread
From: tip-bot2 for Yejune Deng @ 2021-05-19 9:02 UTC (permalink / raw)
To: linux-tip-commits
Cc: Yejune Deng, Valentin Schneider, Peter Zijlstra (Intel),
x86, linux-kernel
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 570a752b7a9bd03b50ad6420cd7f10092cc11bd3
Gitweb: https://git.kernel.org/tip/570a752b7a9bd03b50ad6420cd7f10092cc11bd3
Author: Yejune Deng <yejune.deng@gmail.com>
AuthorDate: Mon, 10 May 2021 16:10:24 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 19 May 2021 10:51:40 +02:00
lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
is_percpu_thread() more elegantly handles SMP vs UP, and further checks the
presence of PF_NO_SETAFFINITY. This lets us catch cases where
check_preemption_disabled() can race with a concurrent sched_setaffinity().
Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
[Amended changelog]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@arm.com
---
lib/smp_processor_id.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 1c1dbd3..046ac62 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
if (irqs_disabled())
goto out;
- /*
- * Kernel threads bound to a single CPU can safely use
- * smp_processor_id():
- */
- if (current->nr_cpus_allowed == 1)
+ if (is_percpu_thread())
goto out;
#ifdef CONFIG_SMP
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot
2021-05-19 9:02 ` tip-bot2 for Yejune Deng
@ 2021-05-31 10:21 ` Peter Zijlstra
2021-06-01 11:54 ` Valentin Schneider
2021-06-01 14:04 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
0 siblings, 2 replies; 13+ messages in thread
From: Peter Zijlstra @ 2021-05-31 10:21 UTC (permalink / raw)
To: linux-kernel; +Cc: linux-tip-commits, Yejune Deng, Valentin Schneider, x86
On Wed, May 19, 2021 at 09:02:34AM -0000, tip-bot2 for Yejune Deng wrote:
> The following commit has been merged into the sched/core branch of tip:
>
> Commit-ID: 570a752b7a9bd03b50ad6420cd7f10092cc11bd3
> Gitweb: https://git.kernel.org/tip/570a752b7a9bd03b50ad6420cd7f10092cc11bd3
> Author: Yejune Deng <yejune.deng@gmail.com>
> AuthorDate: Mon, 10 May 2021 16:10:24 +01:00
> Committer: Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Wed, 19 May 2021 10:51:40 +02:00
>
> lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed
>
> is_percpu_thread() more elegantly handles SMP vs UP, and further checks the
> presence of PF_NO_SETAFFINITY. This lets us catch cases where
> check_preemption_disabled() can race with a concurrent sched_setaffinity().
>
> Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
> [Amended changelog]
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@arm.com
> ---
> lib/smp_processor_id.c | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
> index 1c1dbd3..046ac62 100644
> --- a/lib/smp_processor_id.c
> +++ b/lib/smp_processor_id.c
> @@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
> if (irqs_disabled())
> goto out;
>
> - /*
> - * Kernel threads bound to a single CPU can safely use
> - * smp_processor_id():
> - */
> - if (current->nr_cpus_allowed == 1)
> + if (is_percpu_thread())
> goto out;
So my test box was unhappy with all this and started spewing lots of
DEBUG_PREEMPT warns on boot.
This extends 8fb12156b8db6 to cover the new requirement.
---
Subject: sched,init: Fix DEBUG_PREEMPT vs early boot
Extend 8fb12156b8db ("init: Pin init task to the boot CPU, initially")
to cover the new PF_NO_SETAFFINITY requirement.
While there, move wait_for_completion(&kthreadd_done) into kernel_init()
to make it absolutely clear it is the very first thing done by the init
thread.
Fixes: 570a752b7a9b ("lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
init/main.c | 11 ++++++-----
kernel/sched/core.c | 1 +
2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/init/main.c b/init/main.c
index 7b027d9c5c89..e945ec82b8a5 100644
--- a/init/main.c
+++ b/init/main.c
@@ -692,6 +692,7 @@ noinline void __ref rest_init(void)
*/
rcu_read_lock();
tsk = find_task_by_pid_ns(pid, &init_pid_ns);
+ tsk->flags |= PF_NO_SETAFFINITY;
set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
rcu_read_unlock();
@@ -1440,6 +1441,11 @@ static int __ref kernel_init(void *unused)
{
int ret;
+ /*
+ * Wait until kthreadd is all set-up.
+ */
+ wait_for_completion(&kthreadd_done);
+
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
@@ -1520,11 +1526,6 @@ void __init console_on_rootfs(void)
static noinline void __init kernel_init_freeable(void)
{
- /*
- * Wait until kthreadd is all set-up.
- */
- wait_for_completion(&kthreadd_done);
-
/* Now the scheduler is fully set up and can do blocking allocations */
gfp_allowed_mask = __GFP_BITS_MASK;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index adea0b1e8036..ae7737e6c2b2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8867,6 +8867,7 @@ void __init sched_init_smp(void)
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)
BUG();
+ current->flags &= ~PF_NO_SETAFFINITY;
sched_init_granularity();
init_sched_rt_class();
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot
2021-05-31 10:21 ` [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot Peter Zijlstra
@ 2021-06-01 11:54 ` Valentin Schneider
2021-06-01 14:04 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
1 sibling, 0 replies; 13+ messages in thread
From: Valentin Schneider @ 2021-06-01 11:54 UTC (permalink / raw)
To: Peter Zijlstra, linux-kernel; +Cc: linux-tip-commits, Yejune Deng, x86
On 31/05/21 12:21, Peter Zijlstra wrote:
> On Wed, May 19, 2021 at 09:02:34AM -0000, tip-bot2 for Yejune Deng wrote:
>> @@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
>> if (irqs_disabled())
>> goto out;
>>
>> - /*
>> - * Kernel threads bound to a single CPU can safely use
>> - * smp_processor_id():
>> - */
>> - if (current->nr_cpus_allowed == 1)
>> + if (is_percpu_thread())
>> goto out;
>
> So my test box was unhappy with all this and started spewing lots of
> DEBUG_PREEMPT warns on boot.
>
I get these too, though can't recall getting them when testing the
above. I think it's tied with what Frederic found out with copy_process()
copying PF_NO_SETAFFINITY, which it now no longer does.
> This extends 8fb12156b8db6 to cover the new requirement.
>
> ---
> Subject: sched,init: Fix DEBUG_PREEMPT vs early boot
>
> Extend 8fb12156b8db ("init: Pin init task to the boot CPU, initially")
> to cover the new PF_NO_SETAFFINITY requirement.
>
> While there, move wait_for_completion(&kthreadd_done) into kernel_init()
> to make it absolutely clear it is the very first thing done by the init
> thread.
>
> Fixes: 570a752b7a9b ("lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
^ permalink raw reply [flat|nested] 13+ messages in thread
* [tip: sched/core] sched,init: Fix DEBUG_PREEMPT vs early boot
2021-05-31 10:21 ` [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot Peter Zijlstra
2021-06-01 11:54 ` Valentin Schneider
@ 2021-06-01 14:04 ` tip-bot2 for Peter Zijlstra
1 sibling, 0 replies; 13+ messages in thread
From: tip-bot2 for Peter Zijlstra @ 2021-06-01 14:04 UTC (permalink / raw)
To: linux-tip-commits
Cc: Peter Zijlstra (Intel),
Valentin Schneider, Borislav Petkov, x86, linux-kernel
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 15faafc6b449777a85c0cf82dd8286c293fed4eb
Gitweb: https://git.kernel.org/tip/15faafc6b449777a85c0cf82dd8286c293fed4eb
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 31 May 2021 12:21:13 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 01 Jun 2021 16:00:11 +02:00
sched,init: Fix DEBUG_PREEMPT vs early boot
Extend 8fb12156b8db ("init: Pin init task to the boot CPU, initially")
to cover the new PF_NO_SETAFFINITY requirement.
While there, move wait_for_completion(&kthreadd_done) into kernel_init()
to make it absolutely clear it is the very first thing done by the init
thread.
Fixes: 570a752b7a9b ("lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/YLS4mbKUrA3Gnb4t@hirez.programming.kicks-ass.net
---
init/main.c | 11 ++++++-----
kernel/sched/core.c | 1 +
2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/init/main.c b/init/main.c
index 7b027d9..e945ec8 100644
--- a/init/main.c
+++ b/init/main.c
@@ -692,6 +692,7 @@ noinline void __ref rest_init(void)
*/
rcu_read_lock();
tsk = find_task_by_pid_ns(pid, &init_pid_ns);
+ tsk->flags |= PF_NO_SETAFFINITY;
set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id()));
rcu_read_unlock();
@@ -1440,6 +1441,11 @@ static int __ref kernel_init(void *unused)
{
int ret;
+ /*
+ * Wait until kthreadd is all set-up.
+ */
+ wait_for_completion(&kthreadd_done);
+
kernel_init_freeable();
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
@@ -1520,11 +1526,6 @@ void __init console_on_rootfs(void)
static noinline void __init kernel_init_freeable(void)
{
- /*
- * Wait until kthreadd is all set-up.
- */
- wait_for_completion(&kthreadd_done);
-
/* Now the scheduler is fully set up and can do blocking allocations */
gfp_allowed_mask = __GFP_BITS_MASK;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3d25272..e205c19 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8862,6 +8862,7 @@ void __init sched_init_smp(void)
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)
BUG();
+ current->flags &= ~PF_NO_SETAFFINITY;
sched_init_granularity();
init_sched_rt_class();
^ permalink raw reply related [flat|nested] 13+ messages in thread
end of thread, other threads:[~2021-06-01 14:05 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-10 15:10 [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Valentin Schneider
2021-05-10 15:10 ` [PATCH 1/2] sched: Make the idle task quack like a per-CPU kthread Valentin Schneider
2021-05-10 15:57 ` Valentin Schneider
2021-05-11 7:32 ` Ingo Molnar
2021-05-11 9:33 ` Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Valentin Schneider
2021-05-10 15:10 ` [PATCH 2/2] lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed Valentin Schneider
2021-05-19 8:09 ` [tip: sched/core] " tip-bot2 for Yejune Deng
2021-05-19 9:02 ` tip-bot2 for Yejune Deng
2021-05-31 10:21 ` [PATCH] sched,init: Fix DEBUG_PREEMPT vs early boot Peter Zijlstra
2021-06-01 11:54 ` Valentin Schneider
2021-06-01 14:04 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-05-12 11:00 ` [PATCH 0/2] sched: Address idle task vs pcpu kthread checks Peter Zijlstra
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