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Subject[RFC 07/10] lib/cpumask: Introduce cpumask_not_dying_but()
Date
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
--
2.31.1
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