linux-kernel - Re: [PATCH] ring-buffer: Add rb_check_bpage in __rb_allocate

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Message-ID: <CAJRQjodMzSAJd23F=RRhR=d2H=D3vWMvCbU9JYdGNQ9MTkpmmw@mail.gmail.com>
Date:   Wed, 14 Oct 2020 23:48:05 +0800
From:   Qiujun Huang <hqjagain@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ring-buffer: Add rb_check_bpage in __rb_allocate_pages

On Wed, Oct 14, 2020 at 11:38 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 14 Oct 2020 23:16:14 +0800
> Qiujun Huang <hqjagain@...il.com> wrote:
>
> > It may be better to check each page is aligned by 4 bytes. The 2
> > least significant bits of the address will be used as flags.
> >
> > Signed-off-by: Qiujun Huang <hqjagain@...il.com>
> > ---
> >  kernel/trace/ring_buffer.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index 93ef0ab6ea20..9dec7d58b177 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -1420,7 +1420,8 @@ static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
> >       return 0;
> >  }
> >
> > -static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
> > +static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
> > +             long nr_pages, struct list_head *pages, int cpu)
> >  {
> >       struct buffer_page *bpage, *tmp;
> >       bool user_thread = current->mm != NULL;
> > @@ -1464,6 +1465,8 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
> >               if (!bpage)
> >                       goto free_pages;
> >
> > +             rb_check_bpage(cpu_buffer, bpage);
> > +
> >
>
> Why add it here, and not just add this check to the scan in
> rb_check_pages()?

rb_head_page_deactivate() in rb_check_pages() will clear the 2 LSB first.

>
> -- Steve