Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support

From: Florian Fainelli <f.fainelli@gmail.com>
To: Alexander Sverdlin <alexander.sverdlin@nokia.com>,
	Qais Yousef <qais.yousef@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support
Date: Wed, 10 Mar 2021 08:14:07 -0800	[thread overview]
Message-ID: <05608bc8-f44d-5f91-15ab-af00c59b53e6@gmail.com> (raw)
In-Reply-To: <3eecf51d-b189-9e8b-f19d-a49d0764aae5@nokia.com>

On 3/9/2021 11:23 PM, Alexander Sverdlin wrote:
> Hi!
> 
> On 09/03/2021 18:42, Qais Yousef wrote:
>>>> I tried on 5.12-rc2 and 5.11 but couldn't reproduce the problem using your
>> I still can't reproduce on 5.12-rc2.
>>
>> I do have CONFIG_ARM_MODULE_PLTS=y. Do you need to do something else after
>> loading the module? I tried starting ftrace, but maybe there's a particular
>> combination required?
> 
> You need to load a BIG module, so big that it has no place in the modules area
> any more and goes to vmalloc area.

You absolutely need a very big module maybe more than one. When I tested
this, I could use the two proprietary modules (*sigh*) that I needed to
exercise against and loading one but not the other was not enough to
make the second module loading spill into vmalloc space.

> 
>>>> instructions on the other email. But most likely because I'm hitting another
>>>> problem that could be masking it. I'm not sure it is related or just randomly
>>>> happened to hit it.
>>>>
>>>> Did you see something similar?
>>> [...]
>>>
>>>> 	[    0.000000] [<c1b01a38>] (ftrace_bug) from [<c046316c>] (ftrace_process_locs+0x2b0/0x518)
>>>> 	[    0.000000]  r7:c3817ac4 r6:c38040c0 r5:00000a3c r4:000134e4
>>>> 	[    0.000000] [<c0462ebc>] (ftrace_process_locs) from [<c2b25240>] (ftrace_init+0xc8/0x174)
>>>> 	[    0.000000]  r10:c2ffa000 r9:c2be8a78 r8:c2c5d1fc r7:c2c0c208 r6:00000001 r5:c2d0908c
>>>> 	[    0.000000]  r4:c362f518
>>>> 	[    0.000000] [<c2b25178>] (ftrace_init) from [<c2b00e14>] (start_kernel+0x2f4/0x5b8)
>>>> 	[    0.000000]  r9:c2be8a78 r8:dbfffec0 r7:00000000 r6:c36385cc r5:c2d08f00 r4:c2ffa000
>>>> 	[    0.000000] [<c2b00b20>] (start_kernel) from [<00000000>] (0x0)
>>> This means, FTRACE has more problems with your kernel/compiler/platform, I've addressed similar issue
>>> in the past, but my patch should be long merged:
>>>
>>> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1817963.html
>>>
>>> Could it be the same problem as here:
>>> https://www.spinics.net/lists/arm-kernel/msg854022.html
>>>
>>> Seems that the size check deserves something line BUILD_BUG_ON() with FTRACE...
>> So I only see this when I convert all modules to be built-in
>>
>> 	sed -i 's/=m/=y/' .config
>>
>> FWIW, I see the problem with your patch applied too. Trying to dig more into
>> it..
> 
> Then it's definitely the problem explained in the second link. If you have THUMB2 kernel, maybe
> you have to switch to ARM.
> 

-- 
Florian