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Date: Thu, 15 Oct 2020 00:32:28 +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 Thu, Oct 15, 2020 at 12:11 AM Steven Rostedt <rostedt@...dmis.org> wrote: > > On Wed, 14 Oct 2020 23:48:05 +0800 > Qiujun Huang <hqjagain@...il.com> wrote: > > > 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. > > > > Well, you could just add another scan there, but if you want to do it this > way, then remove passing the int cpu to these functions, and use the > cpu_buffer->cpu, as keeping the cpu is just redundant. Get it. > > Also, did you see an issue? This check is more of me being paranoid to No, I'm a little paranoid too following the code :-) > make sure we don't crash later. I've honestly never seen it trigger. > > -- Steve
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