linux-kernel - Re: [GIT PULL] ftrace: Check if pages were allocated before calling free

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Date:   Thu, 1 Apr 2021 16:53:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] ftrace: Check if pages were allocated before calling
 free_pages()

On Thu, 1 Apr 2021 13:18:59 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Apr 1, 2021 at 1:07 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Wed, 31 Mar 2021 11:03:21 -0700
> > Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> >
> > > @@ -6231,7 +6231,8 @@ static int ftrace_process_locs(struct module *mod,
> > >               if (!addr)
> > >                       continue;
> > >
> > > -             if (pg->index == pg->size) {
> > > +             end_offset = (pg->index+1) * sizeof(pg->records[0]);
> > > +             if (end_offset < PAGE_SIZE << pg->order) {
> >
> > I believe that needs to be:
> >
> >         if (end_offset >= PAGE_SIZE << pg->order) {
> 

[..]

> which will be
> 
>         end_offset = (3+1) * 1024;
> 
> ie 4096. That just means that the struct fill fill things _up_to_ the
> end of the page.
> 
> So only when the end_offset is strictly larger than the page would it
> have overflowed the allocation.

Ah, I forgot about the "+1" you added to the pg->index, which would make it
equivalent to replacing:

	if (pg->index + 1 > pg->size) {


Will update and add your SOB.

Thanks,

-- Steve