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

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On Mon, Oct 10, 2016 at 4:59 PM, Kees Cook <keescook@chromium.org> wrote:
> On Sun, Oct 9, 2016 at 10:15 AM, Joel Fernandes <joelaf@google.com> wrote:
>> On Fri, Oct 7, 2016 at 10:28 PM, Joel Fernandes <joelaf@google.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@google.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.

Oh, also, this new flag needs to be explosed as a module parameter and
Device Tree flag as well, so it's available for more than just the
dummy driver. :)

-Kees

-- 
Kees Cook
Nexus Security

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Thread

[RFC 0/7] pstore: Improve performance of ftrace backend with ramoops Joel Fernandes <joelaf@google.com> - 2016-10-08 07:30 +0200
  [PATCH 2/7] pstore: locking: dont lock unless caller asks to Joel Fernandes <joelaf@google.com> - 2016-10-08 07:30 +0200
    Re: [PATCH 2/7] pstore: locking: dont lock unless caller asks to Kees Cook <keescook@chromium.org> - 2016-10-11 01:50 +0200
      Re: [PATCH 2/7] pstore: locking: dont lock unless caller asks to Joel Fernandes <joelaf@google.com> - 2016-10-11 17:10 +0200
  [PATCH 3/7] pstore: Remove case of PSTORE_TYPE_PMSG write using deprecated function Joel Fernandes <joelaf@google.com> - 2016-10-08 07:30 +0200
    Re: [PATCH 3/7] pstore: Remove case of PSTORE_TYPE_PMSG write using  deprecated function Kees Cook <keescook@chromium.org> - 2016-10-11 02:00 +0200
      Re: [PATCH 3/7] pstore: Remove case of PSTORE_TYPE_PMSG write using  deprecated function Joel Fernandes <joelaf@google.com> - 2016-10-11 16:50 +0200
  [PATCH 7/7] pstore: Merge per-CPU ftrace zones into one zone for output Joel Fernandes <joelaf@google.com> - 2016-10-08 07:30 +0200
  [PATCH 1/7] pstore: Make spinlock per zone instead of global Joel Fernandes <joelaf@google.com> - 2016-10-08 07:30 +0200
    Re: [PATCH 1/7] pstore: Make spinlock per zone instead of global Joel Fernandes <joelaf@google.com> - 2016-10-08 07:50 +0200
    Re: [PATCH 1/7] pstore: Make spinlock per zone instead of global Kees Cook <keescook@chromium.org> - 2016-10-11 02:00 +0200
  [PATCH 4/7] pstore: Make ramoops_init_przs generic for other prz arrays Joel Fernandes <joelaf@google.com> - 2016-10-08 07:40 +0200
    Re: [PATCH 4/7] pstore: Make ramoops_init_przs generic for other prz arrays Kees Cook <keescook@chromium.org> - 2016-10-11 02:00 +0200
  [PATCH 6/7] pstore: Add support to store timestamp counter in ftrace records Joel Fernandes <joelaf@google.com> - 2016-10-08 07:40 +0200
  [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones Joel Fernandes <joelaf@google.com> - 2016-10-08 07:40 +0200
    Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones Joel Fernandes <joelaf@google.com> - 2016-10-09 19:20 +0200
      Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones Kees Cook <keescook@chromium.org> - 2016-10-11 02:00 +0200
        Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones Kees Cook <keescook@chromium.org> - 2016-10-11 02:10 +0200
  Re: [RFC 0/7] pstore: Improve performance of ftrace backend with  ramoops Steven Rostedt <rostedt@goodmis.org> - 2016-10-11 12:00 +0200

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