linux-kernel - Re: arm64: pstore: printk causing hang during boot in __memcpy

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Date:   Wed, 1 Aug 2018 22:46:06 +0530
From:   Ivid Suvarna <ivid.suvarna@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason Baron <jbaron@...hat.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Joe Perches <joe@...ches.com>, linux-arm-msm@...r.kernel.org
Subject: Re: arm64: pstore: printk causing hang during boot in __memcpy_toio
 with pstore enabled

On Wed, Aug 1, 2018 at 6:49 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 08/01/2018 05:35 AM, Ivid Suvarna wrote:
>>
>> Hi,
>>
>> When pstore is enabled and a *pr_info(any printk) in
>> __memcpy_toio(arch/arm64/kernel/io.c)* is added, kernel wont boot and
>> just hangs.
>>
>> The path where __memcpy_toio is called is below:
>>
>> ->persistent_ram_update
>>    -> memcpy_toio
>>      -> __memcpy_toio
>>
>> I tried with trace_printk and kernel boots fine. I understand that
>> printk has overhead, but is this expected when we use some printk
>> statement in __memcpy_toio?
>>
>
> I think the problem may be that the printk() output is copied to pstore.
> Since pstore calls memcpy_toio(), you get a nice recursion if you add a
> printk() call to it.
>

Is there any solution to this other than not adding printk :p