Commit 60490e79 authored Feb 09, 2022 by Zhipeng Xie Committed by Peter Zijlstra Apr 19, 2022

perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

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



Fixes: 906010b2 ("perf_event: Provide vmalloc() based mmap() backing")
Signed-off-by: Zhipeng Xie <xiezhipeng1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220209145417.6495-1-xiezhipeng1@huawei.com

parent b2d229d4

kernel/events/core.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -6247,7 +6247,7 @@ 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;
		}

kernel/events/internal.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -116,6 +116,11 @@ static inline int page_order(struct perf_buffer *rb)
		}
		#endif

		static inline 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));

kernel/events/ring_buffer.c

+0 −5

Original line number	Diff line number	Diff line
		@@ -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)
		{