linux-kernel - Re: [PATCH 1/2] tracing: Simplify the max length test when using the filtering temp buffer

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Message-ID: <CAHk-=wj3S_DxdQkXVaQKcUBCyjiYHC3KqPBTMY151rvZzqKVFQ@mail.gmail.com>
Date:   Wed, 9 Jun 2021 15:21:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] tracing: Simplify the max length test when using the
 filtering temp buffer

On Wed, Jun 9, 2021 at 3:05 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
>                 val = this_cpu_inc_return(trace_buffered_event_cnt);
> -               if ((len < (PAGE_SIZE - sizeof(*entry) - sizeof(entry->array[0]))) && val == 1) {
> +               if (val == 1 && unlikely(len < max_len)) {

unlikely? No.

Also, I still think that "len < max_len" should actually be "len <=
max_len".  It should be ok to use the whole page, no?

Unless there is some *other* overflow issue, and "len" doesn't contain
a terminating NUL character or something like that.

              Linus