Re: Crash in msm serial on dragonboard with ftrace bootargs

Sai Prakash Ranjan
2018-10-17T11:38:09Z

On 10/17/2018 3:43 PM, Joel Fernandes wrote:
> Hi Kees,
>
> On Tue, Oct 16, 2018 at 10:02:53AM -0700, Kees Cook wrote:
>> On Tue, Oct 16, 2018 at 8:29 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>>> On Tue, 16 Oct 2018 17:08:25 +0530
>>> Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> wrote:
>>>> One more thing is for pstore dmesg-ramoops, I had to change
>>>> late_initcall to postcore_initcall which brings the question as to why
>>>> we changed to late_initcall?
>>>> Simple git blame shows to support crypto compress api, but is it really
>>>> helpful? A lot of boottime issues can be caught with pstore enabled at
>>>> postcore_initcall rather than late_initcall, this backtrace
>>>> is just one example. Is there any way we could change this?
>>>
>>> Does it break if the crypto is not initialized? Perhaps add a command
>>> line flag to have it happen earlier:
>>>
>>> ramoops=earlyinit
>>>
>>> and add a postcore_initcall that checks if that flag is set, and if so,
>>> it does the work then, and the late_initcall() will do nothing.
>>>
>>> That way, you can still have unmodified kernels use pstore when it
>>> crashes at boot up.
>>
>> Even better, if we could find a way to make it work with a late
>> initialization of compression (i.e. postcore_initcall() by default
>> means anything caught would be uncompressed, but anything after
>> late_initcall() would be compressed). I'd be very happy to review
>> patches for that!
>
> What do you think about the (untested) patch below? It seems to me that it
> should solve the issue of missing early crash dumps, but I have not tested it
> yet. Sai, would you mind trying it out and let me know if you can see the
> early crash dumps properly now?
>
> ----8<---
> From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> Subject: [RFC] pstore: allocate compression during late_initcall
>
> ramoop's pstore registration (using pstore_register) has to run during
> late_initcall because crypto backend may not be ready during
> postcore_initcall. This causes missing of dmesg crash dumps which could
> have been caught by pstore.
>
> Instead, lets allow ramoops pstore registration earlier, and once crypto
> is ready we can initialize the compression.
>
> Reported-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
> fs/pstore/platform.c | 13 +++++++++++++
> fs/pstore/ram.c | 2 +-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 15e99d5a681d..f09066db2d4d 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -780,6 +780,19 @@ void __init pstore_choose_compression(void)
> }
> }
>
> +static int __init pstore_compression_late_init(void)
> +{
> + /*
> + * Check if any pstore backends registered earlier but did not allocate
> + * for compression because crypto was not ready, if so then initialize
> + * compression.
> + */
> + if (psinfo && !tfm)
> + allocate_buf_for_compression();
> + return 0;
> +}
> +late_initcall(pstore_compression_late_init);
> +
> module_param(compress, charp, 0444);
> MODULE_PARM_DESC(compress, "Pstore compression to use");
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index bbd1e357c23d..98e48d1a9776 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -940,7 +940,7 @@ static int __init ramoops_init(void)
> ramoops_register_dummy();
> return platform_driver_register(&ramoops_driver);
> }
> -late_initcall(ramoops_init);
> +postcore_initcall(ramoops_init);
>
> static void __exit ramoops_exit(void)
> {
>

Yes I could see the early crash dump. Also I tested with different
compression (LZO) instead of deflate just to be sure and it works fine,
thanks :)

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>

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