linux-kernel - [PATCH v2] bpf: Simplify code by using for_each_cpu

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Message-Id: <20220907155746.1750329-1-punit.agrawal@bytedance.com>
Date:   Wed,  7 Sep 2022 16:57:46 +0100
From:   Punit Agrawal <punit.agrawal@...edance.com>
To:     ast@...nel.org
Cc:     Punit Agrawal <punit.agrawal@...edance.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, zhoufeng.zf@...edance.com,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, jolsa@...nel.org
Subject: [PATCH v2] bpf: Simplify code by using for_each_cpu_wrap()

In the percpu freelist code, it is a common pattern to iterate over
the possible CPUs mask starting with the current CPU. The pattern is
implemented using a hand rolled while loop with the loop variable
increment being open-coded.

Simplify the code by using for_each_cpu_wrap() helper to iterate over
the possible cpus starting with the current CPU. As a result, some of
the special-casing in the loop also gets simplified.

No functional change intended.

Signed-off-by: Punit Agrawal <punit.agrawal@...edance.com>
---
v1 -> v2:
* Fixed the incorrect transformation changing semantics of __pcpu_freelist_push_nmi()

Previous version -
v1: https://lore.kernel.org/all/20220817130807.68279-1-punit.agrawal@bytedance.com/

 kernel/bpf/percpu_freelist.c | 48 ++++++++++++------------------------
 1 file changed, 16 insertions(+), 32 deletions(-)

diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
index 00b874c8e889..b6e7f5c5b9ab 100644
--- a/kernel/bpf/percpu_freelist.c
+++ b/kernel/bpf/percpu_freelist.c
@@ -58,23 +58,21 @@ static inline void ___pcpu_freelist_push_nmi(struct pcpu_freelist *s,
 {
 	int cpu, orig_cpu;
 
-	orig_cpu = cpu = raw_smp_processor_id();
+	orig_cpu = raw_smp_processor_id();
 	while (1) {
-		struct pcpu_freelist_head *head;
+		for_each_cpu_wrap(cpu, cpu_possible_mask, orig_cpu) {
+			struct pcpu_freelist_head *head;
 
-		head = per_cpu_ptr(s->freelist, cpu);
-		if (raw_spin_trylock(&head->lock)) {
-			pcpu_freelist_push_node(head, node);
-			raw_spin_unlock(&head->lock);
-			return;
+			head = per_cpu_ptr(s->freelist, cpu);
+			if (raw_spin_trylock(&head->lock)) {
+				pcpu_freelist_push_node(head, node);
+				raw_spin_unlock(&head->lock);
+				return;
+			}
 		}
-		cpu = cpumask_next(cpu, cpu_possible_mask);
-		if (cpu >= nr_cpu_ids)
-			cpu = 0;
 
 		/* cannot lock any per cpu lock, try extralist */
-		if (cpu == orig_cpu &&
-		    pcpu_freelist_try_push_extra(s, node))
+		if (pcpu_freelist_try_push_extra(s, node))
 			return;
 	}
 }
@@ -125,13 +123,12 @@ static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
 {
 	struct pcpu_freelist_head *head;
 	struct pcpu_freelist_node *node;
-	int orig_cpu, cpu;
+	int cpu;
 
-	orig_cpu = cpu = raw_smp_processor_id();
-	while (1) {
+	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
 		head = per_cpu_ptr(s->freelist, cpu);
 		if (!READ_ONCE(head->first))
-			goto next_cpu;
+			continue;
 		raw_spin_lock(&head->lock);
 		node = head->first;
 		if (node) {
@@ -140,12 +137,6 @@ static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
 			return node;
 		}
 		raw_spin_unlock(&head->lock);
-next_cpu:
-		cpu = cpumask_next(cpu, cpu_possible_mask);
-		if (cpu >= nr_cpu_ids)
-			cpu = 0;
-		if (cpu == orig_cpu)
-			break;
 	}
 
 	/* per cpu lists are all empty, try extralist */
@@ -164,13 +155,12 @@ ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
 {
 	struct pcpu_freelist_head *head;
 	struct pcpu_freelist_node *node;
-	int orig_cpu, cpu;
+	int cpu;
 
-	orig_cpu = cpu = raw_smp_processor_id();
-	while (1) {
+	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
 		head = per_cpu_ptr(s->freelist, cpu);
 		if (!READ_ONCE(head->first))
-			goto next_cpu;
+			continue;
 		if (raw_spin_trylock(&head->lock)) {
 			node = head->first;
 			if (node) {
@@ -180,12 +170,6 @@ ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
 			}
 			raw_spin_unlock(&head->lock);
 		}
-next_cpu:
-		cpu = cpumask_next(cpu, cpu_possible_mask);
-		if (cpu >= nr_cpu_ids)
-			cpu = 0;
-		if (cpu == orig_cpu)
-			break;
 	}
 
 	/* cannot pop from per cpu lists, try extralist */
-- 
2.35.1