[PATCH v2] perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

[Zhipeng Xie]

This problem can be reproduced with CONFIG_PERF_USE_VMALLOC enabled on both
x86_64 and aarch64 arch when using sysdig -B(using ebpf)[1].
sysdig -B works fine after rebuilding the kernel with CONFIG_PERF_USE_VMALLOC
disabled.

I tracked it down to the if condition event->rb->nr_pages != nr_pages in
perf_mmap is true when CONFIG_PERF_USE_VMALLOC is enabled where
event->rb->nr_pages = 1 and nr_pages = 2048 resulting perf_mmap to return
-EINVAL.This is because when CONFIG_PERF_USE_VMALLOC is enabled, rb->nr_pages
is always equal to 1.

Arch with CONFIG_PERF_USE_VMALLOC enabled by default:
	arc/arm/csky/mips/sh/sparc/xtensa
Arch with CONFIG_PERF_USE_VMALLOC disabled by default:
	x86_64/aarch64/...

Fix this problem by using data_page_nr.

[1] https://github.com/draios/sysdig

Signed-off-by: Zhipeng Xie <xiezhipeng1@xxxxxxxxxx>
---
 kernel/events/core.c        | 2 +-
 kernel/events/internal.h    | 5 +++++
 kernel/events/ring_buffer.c | 5 -----
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 57c7197838db..370292effd32 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6352,7 +6352,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 again:
 	mutex_lock(&event->mmap_mutex);
 	if (event->rb) {
-		if (event->rb->nr_pages != nr_pages) {
+		if (data_page_nr(event->rb) != nr_pages) {
 			ret = -EINVAL;
 			goto unlock;
 		}
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 082832738c8f..5816c0719dbf 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -116,6 +116,11 @@ static inline int page_order(struct perf_buffer *rb)
 }
 #endif
 
+static int data_page_nr(struct perf_buffer *rb)
+{
+	return rb->nr_pages << page_order(rb);
+}
+
 static inline unsigned long perf_data_size(struct perf_buffer *rb)
 {
 	return rb->nr_pages << (PAGE_SHIFT + page_order(rb));
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 52868716ec35..fb35b926024c 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -859,11 +859,6 @@ void rb_free(struct perf_buffer *rb)
 }
 
 #else
-static int data_page_nr(struct perf_buffer *rb)
-{
-	return rb->nr_pages << page_order(rb);
-}
-
 static struct page *
 __perf_mmap_to_page(struct perf_buffer *rb, unsigned long pgoff)
 {
-- 
2.18.1