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

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Message-ID: <20220318011941.19116-1-xiezhipeng1@huawei.com>
Date:   Thu, 17 Mar 2022 21:19:41 -0400
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: Re: PING: [PATCH v2] perf/core: Fix perf_mmap fail when CONFIG_PERF_USE_VMALLOC enabled

Ping again, sorry for the noise.

On Thu, February 17, 2022 12:54 AM, Zhipeng Xie wrote:
> 
> 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

Best Regards,
Zhipeng Xie