[kvm-unit-tests PATCH 12/24] arm/arm64: Remove spinlocks from on_cpu_async

Andrew Jones
2024-01-24T07:18:53Z

Remove spinlocks from on_cpu_async() by pulling some of their
use into a new function and also by narrowing the locking to a
single on_cpu_info structure by introducing yet another cpumask.

Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
---
lib/arm/asm/smp.h | 4 +++-
lib/arm/smp.c | 37 ++++++++++++++++++++++++++++---------
2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/lib/arm/asm/smp.h b/lib/arm/asm/smp.h
index 9f6d839ab568..f0c0f97a19f8 100644
--- a/lib/arm/asm/smp.h
+++ b/lib/arm/asm/smp.h
@@ -27,9 +27,11 @@ extern bool cpu0_calls_idle;
extern void halt(void);
extern void do_idle(void);

-extern void smp_boot_secondary(int cpu, secondary_entry_fn entry);
extern void on_cpu_async(int cpu, void (*func)(void *data), void *data);
extern void on_cpu(int cpu, void (*func)(void *data), void *data);
extern void on_cpus(void (*func)(void *data), void *data);

+extern void smp_boot_secondary(int cpu, secondary_entry_fn entry);
+extern void smp_boot_secondary_nofail(int cpu, secondary_entry_fn entry);
+
#endif /* _ASMARM_SMP_H_ */
diff --git a/lib/arm/smp.c b/lib/arm/smp.c
index c00fda2efb03..e0872a1a72c2 100644
--- a/lib/arm/smp.c
+++ b/lib/arm/smp.c
@@ -76,12 +76,32 @@ void smp_boot_secondary(int cpu, secondary_entry_fn entry)
spin_unlock(&lock);
}

+void smp_boot_secondary_nofail(int cpu, secondary_entry_fn entry)
+{
+ spin_lock(&lock);
+ if (!cpu_online(cpu))
+ __smp_boot_secondary(cpu, entry);
+ spin_unlock(&lock);
+}
+
struct on_cpu_info {
void (*func)(void *data);
void *data;
cpumask_t waiters;
};
static struct on_cpu_info on_cpu_info[NR_CPUS];
+static cpumask_t on_cpu_info_lock;
+
+static bool get_on_cpu_info(int cpu)
+{
+ return !cpumask_test_and_set_cpu(cpu, &on_cpu_info_lock);
+}
+
+static void put_on_cpu_info(int cpu)
+{
+ int ret = cpumask_test_and_clear_cpu(cpu, &on_cpu_info_lock);
+ assert(ret);
+}

static void __deadlock_check(int cpu, const cpumask_t *waiters, bool *found)
{
@@ -158,22 +178,21 @@ void on_cpu_async(int cpu, void (*func)(void *data), void *data)
assert_msg(cpu != 0 || cpu0_calls_idle, "Waiting on CPU0, which is unlikely to idle. "
"If this is intended set cpu0_calls_idle=1");

- spin_lock(&lock);
- if (!cpu_online(cpu))
- __smp_boot_secondary(cpu, do_idle);
- spin_unlock(&lock);
+ smp_boot_secondary_nofail(cpu, do_idle);

for (;;) {
cpu_wait(cpu);
- spin_lock(&lock);
- if ((volatile void *)on_cpu_info[cpu].func == NULL)
- break;
- spin_unlock(&lock);
+ if (get_on_cpu_info(cpu)) {
+ if ((volatile void *)on_cpu_info[cpu].func == NULL)
+ break;
+ put_on_cpu_info(cpu);
+ }
}
+
on_cpu_info[cpu].func = func;
on_cpu_info[cpu].data = data;
- spin_unlock(&lock);
set_cpu_idle(cpu, false);
+ put_on_cpu_info(cpu);
smp_send_event();
}

--
2.43.0