linux-kernel - PING: [PATCH v2] perf/core: Fix perf_mmap fail when CONFIG_PERF_USE

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Date:   Wed, 16 Feb 2022 11:54:27 -0500
From:   Zhipeng Xie <xiezhipeng1@...wei.com>
To:     <peterz@...radead.org>
CC:     <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <fanwentao@...wei.com>, <jolsa@...hat.com>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <mark.rutland@....com>, <mingo@...hat.com>, <namhyung@...nel.org>,
        <xiezhipeng1@...wei.com>, <xiexiuqi@...wei.com>
Subject: PING: [PATCH v2] perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

Hi, Peter

Could you please review the V2 version?

On Wed, February 9, 2022 10:54 PM, Zhipeng Xie wrote:
> 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@...wei.com>
> ---
>  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

Best Regards,
Zhipeng Xie