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

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Message-ID: <20210609183653.0b77510c@rorschach.local.home>
Date:   Wed, 9 Jun 2021 18:36:53 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.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, 9 Jun 2021 15:21:52 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 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.

Bah, that was suppose to be "likely()" :-p

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

Sure, I was still being paranoid. ;-)

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

No, this is kind of like an internal "malloc", where the caller is
passing in the length via "len" of what it needs.

-- Steve