linux-kernel - Re: [RFC 3/6] pstore: remove max argument from ramoops_get_next

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Date:   Fri, 26 Oct 2018 12:40:28 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC 3/6] pstore: remove max argument from ramoops_get_next_prz

On Fri, Oct 26, 2018 at 08:27:49PM +0100, Kees Cook wrote:
> On Fri, Oct 26, 2018 at 8:22 PM, Joel Fernandes <joel@...lfernandes.org> wrote:
> > On Fri, Oct 26, 2018 at 11:00:39AM -0700, Joel Fernandes (Google) wrote:
> >> From the code flow, the 'max' checks are already being done on the prz
> >> passed to ramoops_get_next_prz. Lets remove it to simplify this function
> >> and reduce its arguments.
> >>
> >> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> >> ---
> >>  fs/pstore/ram.c | 14 ++++++--------
> >>  1 file changed, 6 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> >> index cbfdf4b8e89d..3055e05acab1 100644
> >> --- a/fs/pstore/ram.c
> >> +++ b/fs/pstore/ram.c
> >> @@ -124,14 +124,14 @@ static int ramoops_pstore_open(struct pstore_info *psi)
> >>  }
> >>
> >>  static struct persistent_ram_zone *
> >> -ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
> >> +ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c,
> >>                    u64 *id, enum pstore_type_id *typep, bool update)
> >>  {
> >>       struct persistent_ram_zone *prz;
> >>       int i = (*c)++;
> >>
> >>       /* Give up if we never existed or have hit the end. */
> >> -     if (!przs || i >= max)
> >> +     if (!przs)
> >>               return NULL;
> >>
> >>       prz = przs[i];
> >
> > Ah, looks like I may have introduced an issue here since 'i' isn't checked by
> > the caller for the single prz case, its only checked for the multiple prz
> > cases, so something like below could be folded in. I still feel its better
> > than passing the max argument.
> >
> > Another thought is, even better we could have a different function when
> > there's only one prz and not have to pass an array, just pass the first
> > element? Something like...
> >
> > ramoops_get_next_prz_single(struct persistent_ram_zone *prz, uint *c,
> >                             enum pstore_type_id *typep, bool update)
> > And for the _single  case, we also wouldn't need to pass id so that's another
> > argument less.
> >
> > Let me know what you think, otherwise something like the below will need to
> > be folded in to fix this patch... thanks.
> >
> > ----8<---
> >
> > diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> > index 5702b692bdb9..061d2af2485b 100644
> > --- a/fs/pstore/ram.c
> > +++ b/fs/pstore/ram.c
> > @@ -268,17 +268,19 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
> >                 }
> >         }
> >
> > -       if (!prz_ok(prz))
> > +       if (!prz_ok(prz) && !cxt->console_read_cnt) {
> >                 prz = ramoops_get_next_prz(&cxt->cprz, &cxt->console_read_cnt,
> >                                            record, 0);
> > +       }
> >
> > -       if (!prz_ok(prz))
> > +       if (!prz_ok(prz) && !cxt->pmsg_read_cnt)
> >                 prz = ramoops_get_next_prz(&cxt->mprz, &cxt->pmsg_read_cnt,
> >                                            record, 0);
> >
> >         /* ftrace is last since it may want to dynamically allocate memory. */
> >         if (!prz_ok(prz)) {
> > -               if (!(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)) {
> > +               if (!(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU) &&
> > +                   !cxt->ftrace_read_cnt) {
> >                         prz = ramoops_get_next_prz(cxt->fprzs,
> >                                         &cxt->ftrace_read_cnt, record, 0);
> >                 } else {
> 
> Ah yeah, good catch! I think your added fix is right. I was pondering
> asking you to remove the & on the *_read_cnt and having the caller do
> the increment:
> 
>         while (cxt->dump_read_cnt < cxt->max_dump_cnt && !prz) {
>                 prz = ramoops_get_next_prz(cxt->dprzs, cxt->dump_read_cnt++,
>                                            &record->id,
>                                            &record->type,
>                                            PSTORE_TYPE_DMESG, 1);

Sure, that's better, I'll do that. That we don't have to pass a pointer, the
caller knows about the increment, and its a local variable less. thanks!

 - Joel