From: Jiang Liu <jiang....@huawei.com>
Commit f44310b98ddb7 "smp: Fix SMP function call empty cpu mask race"
introduced field call_function_data->cpumask_ipi to resolve a race
condition in smp_call_function_many().
Later commit 9a46ad6d6df3 "smp: make smp_call_function_many() use logic
similar to smp_call_function_single()" fixed the same issue in another
way when optimizing smp_call_function_many(), which then obsoletes
changes introduced by commit f44310b98ddb7. So revert it.
We may also keep call_function_data->cpumask_ipi field and use it to
optimize smp_call_function_many() as below:
diff --git a/kernel/smp.c b/kernel/smp.c
index fe9f773..dd852fb 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -428,6 +428,8 @@ void smp_call_function_many(const struct cpumask *mask,
csd->info = info;
raw_spin_lock_irqsave(&dst->lock, flags);
+ if (list_empty(&dst->list))
+ cpumask_clear_cpu(cpu, cfd->cpumask_ipi);
list_add_tail(&csd->list, &dst->list);
raw_spin_unlock_irqrestore(&dst->lock, flags);
}
But I have no platforms to verify the optimization effect,
so simpify the code first.
Signed-off-by: Jiang Liu <jiang....@huawei.com>
Cc: Jiang Liu <liu...@gmail.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Wang YanQing <udkni...@gmail.com>
Cc: Shaohua Li <s...@kernel.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Ingo Molnar <mi...@elte.hu>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Paul Gortmaker <paul.gortma...@windriver.com>
Cc: liguang <lig.f...@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org
---
kernel/smp.c | 16 ++--------------
1 file changed, 2 insertions(+), 14 deletions(-)
diff --git a/kernel/smp.c b/kernel/smp.c
index fe9f773..a034712 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -23,7 +23,6 @@ enum {
struct call_function_data {
struct call_single_data __percpu *csd;
cpumask_var_t cpumask;
- cpumask_var_t cpumask_ipi;
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
@@ -47,9 +46,6 @@ hotplug_cfd(struct notifier_block *nfb, unsigned long action,
void *hcpu)
if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
cpu_to_node(cpu)))
return notifier_from_errno(-ENOMEM);
- if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, GFP_KERNEL,
- cpu_to_node(cpu)))
- return notifier_from_errno(-ENOMEM);
cfd->csd = alloc_percpu(struct call_single_data);
if (!cfd->csd) {
free_cpumask_var(cfd->cpumask);
@@ -64,7 +60,6 @@ hotplug_cfd(struct notifier_block *nfb, unsigned long action,
void *hcpu)
case CPU_DEAD:
case CPU_DEAD_FROZEN:
free_cpumask_var(cfd->cpumask);
- free_cpumask_var(cfd->cpumask_ipi);
free_percpu(cfd->csd);
break;
#endif
@@ -255,9 +250,9 @@ int smp_call_function_single(int cpu, smp_call_func_t func,
void *info,
csd = &__get_cpu_var(csd_data);
csd_lock(csd);
-
csd->func = func;
csd->info = info;
+
generic_exec_single(cpu, csd, wait);
} else {
err = -ENXIO; /* CPU not online */
@@ -410,13 +405,6 @@ void smp_call_function_many(const struct cpumask *mask,
if (unlikely(!cpumask_weight(cfd->cpumask)))
return;
- /*
- * After we put an entry into the list, cfd->cpumask may be cleared
- * again when another CPU sends another IPI for a SMP function call, so
- * cfd->cpumask will be zero.
- */
- cpumask_copy(cfd->cpumask_ipi, cfd->cpumask);
-
for_each_cpu(cpu, cfd->cpumask) {
struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
struct call_single_queue *dst =
@@ -433,7 +421,7 @@ void smp_call_function_many(const struct cpumask *mask,
}
/* Send a message to all CPUs in the map */
- arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
+ arch_send_call_function_ipi_mask(cfd->cpumask);
if (wait) {
for_each_cpu(cpu, cfd->cpumask) {
--
1.8.1.2
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