During cpu hot-removing, the dying cpus are still in cpu_online_mask.
On the other hand, A subsystem will migrate its broker from the dying
cpu to a online cpu in its teardown cpuhp_step.
After enabling the teardown of cpus in parallel, cpu_online_mask can not
tell those dying from the real online.
Introducing a function cpumask_not_dying_but() to pick a real online
cpu.
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Price <steven.price@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
To: linux-kernel@vger.kernel.org
---
include/linux/cpumask.h | 3 +++
kernel/cpu.c | 3 +++
lib/cpumask.c | 18 ++++++++++++++++++
3 files changed, 24 insertions(+)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 0d435d0edbcb..d2033a239a07 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -317,6 +317,9 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
return i;
}
+/* for parallel kexec reboot */
+int cpumask_not_dying_but(const struct cpumask *mask, unsigned int cpu);
+
#define CPU_BITS_NONE \
{ \
[0 ... BITS_TO_LONGS(NR_CPUS)-1] = 0UL \
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 90debbe28e85..771e344f8ff9 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1282,6 +1282,9 @@ static void cpus_down_no_rollback(struct cpumask *cpus)
struct cpuhp_cpu_state *st;
unsigned int cpu;
+ for_each_cpu(cpu, cpus)
+ set_cpu_dying(cpu, true);
+
/* launch ap work one by one, but not wait for completion */
for_each_cpu(cpu, cpus) {
st = per_cpu_ptr(&cpuhp_state, cpu);
diff --git a/lib/cpumask.c b/lib/cpumask.c
index 8baeb37e23d3..6474f07ed87a 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -7,6 +7,24 @@
#include <linux/memblock.h>
#include <linux/numa.h>
+/* Used in parallel kexec-reboot cpuhp callbacks */
+int cpumask_not_dying_but(const struct cpumask *mask,
+ unsigned int cpu)
+{
+ unsigned int i;
+
+ if (CONFIG_SHUTDOWN_NONBOOT_CPUS) {
+ cpumask_check(cpu);
+ for_each_cpu(i, mask)
+ if (i != cpu && !cpumask_test_cpu(i, cpu_dying_mask))
+ break;
+ return i;
+ } else {
+ return cpumask_any_but(mask, cpu);
+ }
+}
+EXPORT_SYMBOL(cpumask_not_dying_but);
+
/**
* cpumask_next_wrap - helper to implement for_each_cpu_wrap
* @n: the cpu prior to the place to search
--
2.31.1On Mon, Aug 22, 2022 at 10:15:17AM +0800, Pingfan Liu wrote:
> During cpu hot-removing, the dying cpus are still in cpu_online_mask.
> On the other hand, A subsystem will migrate its broker from the dying
> cpu to a online cpu in its teardown cpuhp_step.
>
> After enabling the teardown of cpus in parallel, cpu_online_mask can not
> tell those dying from the real online.
>
> Introducing a function cpumask_not_dying_but() to pick a real online
> cpu.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> To: linux-kernel@vger.kernel.org
> ---
> include/linux/cpumask.h | 3 +++
> kernel/cpu.c | 3 +++
> lib/cpumask.c | 18 ++++++++++++++++++
> 3 files changed, 24 insertions(+)
>
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index 0d435d0edbcb..d2033a239a07 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -317,6 +317,9 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
> return i;
> }
>
> +/* for parallel kexec reboot */
> +int cpumask_not_dying_but(const struct cpumask *mask, unsigned int cpu);
> +
> #define CPU_BITS_NONE \
> { \
> [0 ... BITS_TO_LONGS(NR_CPUS)-1] = 0UL \
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 90debbe28e85..771e344f8ff9 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1282,6 +1282,9 @@ static void cpus_down_no_rollback(struct cpumask *cpus)
> struct cpuhp_cpu_state *st;
> unsigned int cpu;
>
> + for_each_cpu(cpu, cpus)
> + set_cpu_dying(cpu, true);
> +
> /* launch ap work one by one, but not wait for completion */
> for_each_cpu(cpu, cpus) {
> st = per_cpu_ptr(&cpuhp_state, cpu);
> diff --git a/lib/cpumask.c b/lib/cpumask.c
> index 8baeb37e23d3..6474f07ed87a 100644
> --- a/lib/cpumask.c
> +++ b/lib/cpumask.c
> @@ -7,6 +7,24 @@
> #include <linux/memblock.h>
> #include <linux/numa.h>
>
> +/* Used in parallel kexec-reboot cpuhp callbacks */
> +int cpumask_not_dying_but(const struct cpumask *mask,
> + unsigned int cpu)
> +{
> + unsigned int i;
> +
> + if (CONFIG_SHUTDOWN_NONBOOT_CPUS) {
Hmm... Would it even work? Anyways, the documentation says:
Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
symbol into a C boolean expression, and use it in a normal C conditional:
.. code-block:: c
if (IS_ENABLED(CONFIG_SOMETHING)) {
...
}
> + cpumask_check(cpu);
> + for_each_cpu(i, mask)
> + if (i != cpu && !cpumask_test_cpu(i, cpu_dying_mask))
> + break;
> + return i;
> + } else {
> + return cpumask_any_but(mask, cpu);
> + }
> +}
> +EXPORT_SYMBOL(cpumask_not_dying_but);
I don't like how you create a dedicated function for a random
mask. Dying mask is nothing special, right? What you really
need is probably this:
cpumask_andnot_any_but(mask, cpu_dying_mask, cpu);
Now, if you still think it's worth that, you can add a trivial wrapper
for cpu_dying_mask. (But please pick some other name, because
'not dying but' sounds like a hangover description. :) )
Thanks,
Yury
> +
> /**
> * cpumask_next_wrap - helper to implement for_each_cpu_wrap
> * @n: the cpu prior to the place to search
> --
> 2.31.1
On Mon, Aug 22, 2022 at 07:15:45AM -0700, Yury Norov wrote:
> On Mon, Aug 22, 2022 at 10:15:17AM +0800, Pingfan Liu wrote:
> > During cpu hot-removing, the dying cpus are still in cpu_online_mask.
> > On the other hand, A subsystem will migrate its broker from the dying
> > cpu to a online cpu in its teardown cpuhp_step.
> >
> > After enabling the teardown of cpus in parallel, cpu_online_mask can not
> > tell those dying from the real online.
> >
> > Introducing a function cpumask_not_dying_but() to pick a real online
> > cpu.
> >
> > Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Steven Price <steven.price@arm.com>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
> > Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > To: linux-kernel@vger.kernel.org
> > ---
> > include/linux/cpumask.h | 3 +++
> > kernel/cpu.c | 3 +++
> > lib/cpumask.c | 18 ++++++++++++++++++
> > 3 files changed, 24 insertions(+)
> >
> > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > index 0d435d0edbcb..d2033a239a07 100644
> > --- a/include/linux/cpumask.h
> > +++ b/include/linux/cpumask.h
> > @@ -317,6 +317,9 @@ unsigned int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
> > return i;
> > }
> >
> > +/* for parallel kexec reboot */
> > +int cpumask_not_dying_but(const struct cpumask *mask, unsigned int cpu);
> > +
> > #define CPU_BITS_NONE \
> > { \
> > [0 ... BITS_TO_LONGS(NR_CPUS)-1] = 0UL \
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 90debbe28e85..771e344f8ff9 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -1282,6 +1282,9 @@ static void cpus_down_no_rollback(struct cpumask *cpus)
> > struct cpuhp_cpu_state *st;
> > unsigned int cpu;
> >
> > + for_each_cpu(cpu, cpus)
> > + set_cpu_dying(cpu, true);
> > +
> > /* launch ap work one by one, but not wait for completion */
> > for_each_cpu(cpu, cpus) {
> > st = per_cpu_ptr(&cpuhp_state, cpu);
> > diff --git a/lib/cpumask.c b/lib/cpumask.c
> > index 8baeb37e23d3..6474f07ed87a 100644
> > --- a/lib/cpumask.c
> > +++ b/lib/cpumask.c
> > @@ -7,6 +7,24 @@
> > #include <linux/memblock.h>
> > #include <linux/numa.h>
> >
> > +/* Used in parallel kexec-reboot cpuhp callbacks */
> > +int cpumask_not_dying_but(const struct cpumask *mask,
> > + unsigned int cpu)
> > +{
> > + unsigned int i;
> > +
> > + if (CONFIG_SHUTDOWN_NONBOOT_CPUS) {
>
> Hmm... Would it even work? Anyways, the documentation says:
> Within code, where possible, use the IS_ENABLED macro to convert a Kconfig
> symbol into a C boolean expression, and use it in a normal C conditional:
>
> .. code-block:: c
>
> if (IS_ENABLED(CONFIG_SOMETHING)) {
> ...
> }
>
Yes, it shall be like you pointed out.
I changed the code from "#ifdef" style to "if (IS_ENABLED()" style just
before sending out the series. Sorry for the haste without compiling
check again.
>
> > + cpumask_check(cpu);
> > + for_each_cpu(i, mask)
> > + if (i != cpu && !cpumask_test_cpu(i, cpu_dying_mask))
> > + break;
> > + return i;
> > + } else {
> > + return cpumask_any_but(mask, cpu);
> > + }
> > +}
> > +EXPORT_SYMBOL(cpumask_not_dying_but);
>
> I don't like how you create a dedicated function for a random
> mask. Dying mask is nothing special, right? What you really
Yes, I agree.
> need is probably this:
> cpumask_andnot_any_but(mask, cpu_dying_mask, cpu);
>
That is it.
> Now, if you still think it's worth that, you can add a trivial wrapper
> for cpu_dying_mask. (But please pick some other name, because
> 'not dying but' sounds like a hangover description. :) )
>
I think that since even if !IS_ENABLED(CONFIG_SHUTDOWN_NONBOOT_CPUS),
cpumask_andnot_any_but(mask, cpu_dying_mask, cpu) can work properly,
so replacing the callsite with "cpumask_andnot() + cpumask_any_but()"
will be a choice.
Appreciate for your help.
Thanks,
Pingfan
> Thanks,
> Yury
>
> > +
> > /**
> > * cpumask_next_wrap - helper to implement for_each_cpu_wrap
> > * @n: the cpu prior to the place to search
> > --
> > 2.31.1
© 2016 - 2026 Red Hat, Inc.