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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Tue, 30 Oct 2018 21:19:17 -0700
Message-ID: <CAEXW_YTcFzH-5SvT12xrJVUsNp=tgr8E0iuGB2ec76unTHwNJA@mail.gmail.com>
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()
To:     =?UTF-8?B?UGVuZzE1IFdhbmcg546L6bmP?= <wangpeng15@xiaomi.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "vipwangerxiao@gmail.com" <vipwangerxiao@gmail.com>
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On Tue, Oct 30, 2018 at 8:57 PM, Peng15 Wang =E7=8E=8B=E9=B9=8F <wangpeng15=
@xiaomi.com> wrote:
>
>>From: Joel Fernandes <joel@joelfernandes.org>
>>Sent: Wednesday, October 31, 2018 6:16
>>To: Kees Cook
>>Cc: Peng15 Wang =E7=8E=8B=E9=B9=8F; Anton Vorontsov; Colin Cross; Tony Lu=
ck; LKML; vipwangerxiao@gmail.com
>>Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_za=
p()
>>
>>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@joelfernandes.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_SI=
G),
>>> >> 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@xiaomi.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 =3D kasprintf(GFP_KERNEL, "ramoops:%s", name);
>>> >>       *prz =3D persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
>>> >> -                               cxt->memtype, 0, label);
>>> >> +                               cxt->memtype, PRZ_FLAG_ZAP_OLD, labe=
l);
>>> >>       if (IS_ERR(*prz)) {
>>> >>               int err =3D 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 +=3D 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 per=
sistent_ram_zone *prz, u32 sig,
>>> >>                       pr_debug("found existing buffer, size %zu, sta=
rt %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 serie=
s 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=3Dpstore/devel&id=3Dac564e023248e3f4d87917b91d12376ddfca5000
>>
>>Cool, it LGTM :)
>>
>>- Joel
>>
>
> Thank you all for these warm help.
>
> This is my first time to submit a patch to community. Feel great!

Congrats and welcome to the mother ship ;-)

 - Joel