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

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Date:   Wed, 31 Oct 2018 03:57:51 +0000
From:   Peng15 Wang 王鹏 <wangpeng15@...omi.com>
To:     Joel Fernandes <joel@...lfernandes.org>,
        Kees Cook <keescook@...omium.org>
CC:     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" <vipwangerxiao@...il.com>
Subject: Re: [PATCH v4] pstore: Avoid duplicate call of persistent_ram_zap()


>From: Joel Fernandes <joel@...lfernandes.org>
>Sent: Wednesday, October 31, 2018 6:16
>To: Kees Cook
>Cc: Peng15 Wang 王鹏; Anton Vorontsov; Colin Cross; Tony Luck; LKML; 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
>

Thank you all for these warm help.

This is my first time to submit a patch to community. Feel great!