linux-kernel - Re: [PATCH] pstore: reset ftrace_read_cnt at ramoops_pstore

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Message-ID: <CAGXu5j+5CXKJ7+vaWgZXVJgFGHFzcwO6-D1iE+wyDcpr+g8jdw@mail.gmail.com>
Date:	Tue, 4 Mar 2014 11:11:11 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Liu ShuoX <shuox.liu@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	Colin Cross <ccross@...roid.com>,
	Anton Vorontsov <anton@...msg.org>,
	yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH] pstore: reset ftrace_read_cnt at ramoops_pstore_open

On Mon, Mar 3, 2014 at 5:40 PM, Liu ShuoX <shuox.liu@...el.com> wrote:
> On Mon  3.Mar'14 at 11:45:59 -0800, Kees Cook wrote:
>>
>> On Thu, Feb 27, 2014 at 10:37 PM,  <shuox.liu@...el.com> wrote:
>>>
>>> From: Liu ShuoX <shuox.liu@...el.com>
>>>
>>> ftrace_read_cnt need to be reset in open to support mutli times
>>> getting the records.
>>>
>>> Signed-off-by: Liu ShuoX <shuox.liu@...el.com>
>>> ---
>>>  fs/pstore/ram.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
>>> index fa8cef2..a5d0cab 100644
>>> --- a/fs/pstore/ram.c
>>> +++ b/fs/pstore/ram.c
>>> @@ -101,6 +101,7 @@ static int ramoops_pstore_open(struct pstore_info
>>> *psi)
>>>
>>>         cxt->dump_read_cnt = 0;
>>>         cxt->console_read_cnt = 0;
>>> +       cxt->ftrace_read_cnt = 0;
>>>         return 0;
>>>  }
>>
>>
>> I think we need a separate function for "clear" for the
>> ramoops_context struct. IIUC, we're missing a similar initialization
>> in ramoops_probe, which lacks both console_read_cnt=0 and
>> ftrace_read_cnt=0. Then both places could call this?
>
> Hi Kees,
> Currently, we have only one static ramoops_context named oops_cxt.
> *_read_cnt should be initialized to 0 as default. Need we still add
> such function for 'clear'?

We have the pstore-global "oops_cxt" context. It is "initialized" only
once in ramoops_probe (and seems to needlessly set dump_read_cnt to
0). Otherwise, the context is initialized via ramoops_register_dummy
from module parameters (and initialized to zero with kzalloc).

So, I think my initial comment about "clear" is probably not right,
but that ramoops_pstore_open should be doing that (i.e. your original
patch is close). However, I think I'd like to see the needless zeroing
in ramoops_probe removed, and the "variables that need clearing on
open" documented in comments in "struct ramoops_context". That should
make this code more clear to read next time. :)

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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