linux-kernel - Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones

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Date:   Mon, 10 Oct 2016 16:59:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones

On Sun, Oct 9, 2016 at 10:15 AM, Joel Fernandes <joelaf@...gle.com> wrote:
> On Fri, Oct 7, 2016 at 10:28 PM, Joel Fernandes <joelaf@...gle.com> wrote:
>> If FTRACE_PER_CPU flag is passed to ramoops pdata, split the space into
>> multiple zones depending on the number of CPUs.
>>
>> This speeds up the performance of function tracing by about 280% in my tests as
>> we avoid the locking. The trade off being lesser space available per CPU.  Let
>> the ramoops user decide which option they want based on pdata flag.
>>
>> Signed-off-by: Joel Fernandes <joelaf@...gle.com>
>> ---
>>  fs/pstore/ram.c            | 70 +++++++++++++++++++++++++++++++++++-----------
>>  include/linux/pstore_ram.h |  3 ++
>>  2 files changed, 56 insertions(+), 17 deletions(-)
>>
>> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> [..]
>> @@ -391,14 +418,21 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
>>  {
>>         int i;
>>
>> -       if (!cxt->przs)
>> -               return;
>> +       /* Free dump PRZs */
>> +       if (cxt->przs) {
>> +               for (i = 0; i < cxt->max_dump_cnt; i++)
>> +                       persistent_ram_free(cxt->przs[i]);
>>
>> -       for (i = 0; i < cxt->max_dump_cnt; i++)
>> -               persistent_ram_free(cxt->przs[i]);
>> +               kfree(cxt->przs);
>> +               cxt->max_dump_cnt = 0;
>> +       }
>>
>> -       kfree(cxt->przs);
>> -       cxt->max_dump_cnt = 0;
>> +       /* Free ftrace PRZs */
>> +       if (cxt->fprzs) {
>> +               for (i = 0; i < nr_cpu_ids; i++)
>> +                       persistent_ram_free(cxt->przs[i]);
>
> I am supposed to free fprzs[i] here, instead of przs[i]. Also need to
> check flag and free correct number of zones. Will fix for v2, sorry
> about that.

I think the cpu id needs to be bounds-checked against the size of the
allocation. In theory, CPU hot-plug could grow the number of CPUs
after pstore is initialized.

-Kees

-- 
Kees Cook
Nexus Security