linux-kernel - Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram

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Message-ID: <20181030221605.GA44036@joelaf.mtv.corp.google.com>
Date:   Tue, 30 Oct 2018 15:16:05 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peng Wang <wangpeng15@...omi.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, vipwangerxiao@...il.com
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()

On Tue, Oct 30, 2018 at 02:52:43PM -0700, Kees Cook wrote:
> On Tue, Oct 30, 2018 at 2:38 PM, Joel Fernandes <joel@...lfernandes.org> wrote:
> > On Tue, Oct 30, 2018 at 03:52:34PM +0800, Peng Wang wrote:
> >> When initialing prz with invalid data in buffer(no PERSISTENT_RAM_SIG),
> >> function call path is like this:
> >>
> >> ramoops_init_prz ->
> >> |
> >> |-> persistent_ram_new -> persistent_ram_post_init -> persistent_ram_zap
> >> |
> >> |-> persistent_ram_zap
> >>
> >> As we can see, persistent_ram_zap() is called twice.
> >> We can avoid this by adding an option to persistent_ram_new(), and
> >> only call persistent_ram_zap() when it is needed.
> >>
> >> Signed-off-by: Peng Wang <wangpeng15@...omi.com>
> >> ---
> >>  fs/pstore/ram.c            | 4 +---
> >>  fs/pstore/ram_core.c       | 5 +++--
> >>  include/linux/pstore_ram.h | 1 +
> >>  3 files changed, 5 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> >> index ffcff6516e89..b51901f97dc2 100644
> >> --- a/fs/pstore/ram.c
> >> +++ b/fs/pstore/ram.c
> >> @@ -640,7 +640,7 @@ static int ramoops_init_prz(const char *name,
> >>
> >>       label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
> >>       *prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
> >> -                               cxt->memtype, 0, label);
> >> +                               cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
> >>       if (IS_ERR(*prz)) {
> >>               int err = PTR_ERR(*prz);
> >
> > Looks good to me except the minor comment below:
> >
> >>
> >> @@ -649,8 +649,6 @@ static int ramoops_init_prz(const char *name,
> >>               return err;
> >>       }
> >>
> >> -     persistent_ram_zap(*prz);
> >> -
> >>       *paddr += sz;
> >>
> >>       return 0;
> >> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> >> index 12e21f789194..2ededd1ea1c2 100644
> >> --- a/fs/pstore/ram_core.c
> >> +++ b/fs/pstore/ram_core.c
> >> @@ -505,15 +505,16 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
> >>                       pr_debug("found existing buffer, size %zu, start %zu\n",
> >>                                buffer_size(prz), buffer_start(prz));
> >>                       persistent_ram_save_old(prz);
> >> -                     return 0;
> >> +                     if (!(prz->flags & PRZ_FLAG_ZAP_OLD))
> >> +                             return 0;
> >
> > This could be written differently.
> >
> > We could just do:
> >
> > if (prz->flags & PRZ_FLAG_ZAP_OLD)
> >         persistent_ram_zap(prz);
> >
> > And remove the zap from below below.
> 
> I actually rearranged things a little to avoid additional round-trips
> on the mailing list. :)
> 
> > Since Kees already took this patch, I can just patch this in my series if
> > Kees and you are Ok with this suggestion.
> 
> I've put it up here:
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=pstore/devel&id=ac564e023248e3f4d87917b91d12376ddfca5000

Cool, it LGTM :)

- Joel