Date:   Fri, 4 Mar 2022 11:12:35 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <peda@...ntia.se>, <saravanak@...gle.com>
CC:     <alexandre.belloni@...tlin.com>, <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <du@...ntia.se>,
        <Ludovic.Desroches@...rochip.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <Nicolas.Ferre@...rochip.com>
Subject: Re: Regression: memory corruption on Atmel SAMA5D31

Hi, Peter!

On 3/4/22 12:57, Peter Rosin wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 2022-03-04 07:57, Peter Rosin wrote:
>> On 2022-03-04 04:55, Saravana Kannan wrote:
>>> On Thu, Mar 3, 2022 at 1:17 AM Peter Rosin <peda@...ntia.se> wrote:
>>>>
>>>> On 2022-03-03 04:02, Saravana Kannan wrote:
>>>>> On Wed, Mar 2, 2022 at 4:29 PM Peter Rosin <peda@...ntia.se> wrote:
>>>>>>
>>>>>> Hi!
>>>>>>
>>>>>> I'm seeing a weird problem, and I'd like some help with further
>>>>>> things to try in order to track down what's going on. I have
>>>>>> bisected the issue to
>>>>>>
>>>>>> f9aa460672c9 ("driver core: Refactor fw_devlink feature")
>>>>>
>>>>> I skimmed through your email and I'll read it more closely tomorrow,
>>>>> but it wasn't clear if you see this on Linus's tip of the tree too.
>>>>> Asking because of:
>>>>> https://lore.kernel.org/lkml/20210930085714.2057460-1-yangyingliang@huawei.com/
>>>>>
>>>>> Also, a couple of other data points that _might_ help. Try kernel
>>>>> command line option fw_devlink=permissive vs fw_devlink=on (I forget
>>>>> if this was the default by 5.10) vs fw_devlink=off.
>>>>>
>>>>> I'm expecting "off" to fix the issue for you. But if permissive vs on
>>>>> shows a difference driver issues would start becoming a real
>>>>> possibility.
>>>>>
>>>>> -Saravana
>>>>
>>>> Thanks for the quick reply! I don't think I tested the very tip of
>>>> Linus tree before, only latest rc or something like that, but now I
>>>> have. I.e.
>>>>
>>>> 5859a2b19911 ("Merge branch 'ucount-rlimit-fixes-for-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace")
>>>>
>>>> It would have been typical if an issue that existed for a couple of
>>>> years had been fixed the last few weeks, but alas, no.
>>>>
>>>> On that kernel, and with whatever the default fw_devlink value is, the
>>>
>>> It's fw_devlink=on by default from at least 5.12-rc4 or so.
>>>
>>>> issue is there. It's a bit hard to tell if the incident probability
>>>> is the same when trying fw_devlink arguments, but roughly so, and I
>>>> do not have to wait for long to get a bad hash with the first
>>>> reproducer
>>>>
>>>>    while :; do cat testfile | sha256sum; done
>>>>
>>>> The output is typical:
>>>> 78464c59faa203413aceb5f75de85bbf4cde64f21b2d0449a2d72cd2aadac2a3  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> e03c5524ac6d16622b6c43f917aae730bc0793643f461253c4646b860c1a7215  -
>>>> 1b8db6218f481cb8e4316c26118918359e764cc2c29393fd9ef4f2730274bb00  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 7d60bf848911d3b919d26941be33c928c666e9e5666f392d905af2d62d400570  -
>>>> 212e1fe02c24134857ffb098f1834a2d87c655e0e5b9e08d4929f49a070be97c  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 7e33e751eb99a0f63b4f7d64b0a24f3306ffaf7c4bc4b27b82e5886c8ea31bc3  -
>>>> d7a1f08aa9d0374d46d828fc3582f5927e076ff229b38c28089007cd0599c645  -
>>>> 4fc963b7c7b14df9d669500f7c062bf378ff2751f705bb91eecd20d2f896f6fe  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>> 9360d886046c12d983b8bc73dd22302c57b0aafe58215700604fa977b4715fbe  -
>>>> 4f9173f63cb2e13d1470e59e1b5c657f3b0f4f2e9a55ab6facffbb03f34ce04d  -
>>>>
>>>> Setting fw_devlink=off makes no difference, AFAICT.
>>>
>>> By this, I'm assuming you set fw_devlink=off in the kernel command
>>> line and you still saw the corruption.
>>
>> Yes. On a bad kernel it's the same with all of the following kernel
>> command lines.
>>
>> console=ttyS0,115200 rw oops=panic panic=30 fw_devlink=on ip=none root=ubi0:rootfs ubi.mtd=6 rootfstype=ubifs noinitrd mtdparts=atmel_nand:256k(at91bootstrap),384k(barebox),256k@...k(bareboxenv),256k(bareboxenv2),128k@...6k(oftree),5M@2M(kernel),248M@8M(rootfs),-@...M(ovlfs)
>>
>> console=ttyS0,115200 rw oops=panic panic=30 fw_devlink=off ip=none root=ubi0:rootfs ubi.mtd=6 rootfstype=ubifs noinitrd mtdparts=atmel_nand:256k(at91bootstrap),384k(barebox),256k@...k(bareboxenv),256k(bareboxenv2),128k@...6k(oftree),5M@2M(kernel),248M@8M(rootfs),-@...M(ovlfs)
>>
>> console=ttyS0,115200 rw oops=panic panic=30 fw_devlink=permissive ip=none root=ubi0:rootfs ubi.mtd=6 rootfstype=ubifs noinitrd mtdparts=atmel_nand:256k(at91bootstrap),384k(barebox),256k@...k(bareboxenv),256k(bareboxenv2),128k@...6k(oftree),5M@2M(kernel),248M@8M(rootfs),-@...M(ovlfs)
>>
>>> If that's the case, I can't see how this could possibly have anything
>>> to do with:
>>> f9aa460672c9 ("driver core: Refactor fw_devlink feature")
>>>
>>> If you look at fw_devlink_link_device(), you'll see that the function
>>> is NOP if fw_devlink=off (the !fw_devlink_flags check). And from
>>> there, the rest of the code in the series doesn't run because more
>>> fields wouldn't get set, etc. That pretty much disables ALL the code
>>> in the entire series. The only remaining diff would be header file
>>> changes where I add/remove fields. But that's unlikely to cause any
>>> issues here because I'm either deleting fields that aren't used or
>>> adding fields that won't be used (with fw_devlink=off). I think the
>>> patch was just causing enough timing changes that it's masking the
>>> real issue.
>>
>> When I compare fw_devlink_link_device() from before and after
>> f9aa460672c9 ("driver core: Refactor fw_devlink feature")
>> I notice that you also removed an unconditional call to
>> device_link_add_missing_supplier_links() that was live before,
>> regardless of any fw_devlink parameter.
>>
>> I don't know if that's relevant. Is it?
>>
>> Not knowing this code at all, and without any serious attempt
>> at reading it, from here the comment of that removed function
>> sure looks like it might cause a different ordering before and
>> after the patch that is not restored with any fw_devlink
>> argument.
> 
> It appears that the device_link_add_missing_supplier_links() difference
> is not relevant after all. What actually happened in the header file in
> the "bad" commit was that two fields were removed (none added). Like so:
> 
>  struct dev_links_info {
>         struct list_head suppliers;
>         struct list_head consumers;
> -       struct list_head needs_suppliers;
>         struct list_head defer_sync;
> -       bool need_for_probe;
>         enum dl_dev_state status;
>  };
> 
> If I restore those fields on a bad kernel, the issue is no longer
> visible. That is true for the first bad kernel, i.e.
> 
> f9aa460672c9 ("driver core: Refactor fw_devlink feature")
> 
> and for tip of Linus as of recently, i.e.
> 
> 5859a2b19911 ("Merge branch 'ucount-rlimit-fixes-for-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace")
> 
> Which is of course insane and a whole different level of bad. WTF!?!
> 
> I wonder if I can dig out the old SAMA5D31 evaluation kit and reproduce
> there? I think that's next on the list...
> 

I have a sama5d3_xplained that uses a SAMA5D36 and has a 256MBytes DDR2 and a
256MBytes NAND Flash. I tried a test with a 200MB file, rootfs on sdcard and
I couldn't reproduce the bug. I'm using Linus's latest kernel:
38f80f42147f (HEAD, origin/master, origin/HEAD) MAINTAINERS: Remove dead patchwork link

root@...a5d3-xplained-sd:~# dd if=/dev/urandom of=testfile bs=1024 count=200000
200000+0 records in
200000+0 records out
204800000 bytes (205 MB, 195 MiB) copied, 37.6424 s, 5.4 MB/s
root@...a5d3-xplained-sd:~# for i in 1 2 3 4 5 6 7 8; do cat testfile | sha256sum; done
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
2a4f1534aec6ace9d68f2f42fa28c1f1fe7bd281f960f2218797557aa41fe8de  -
root@...a5d3-xplained-sd:~# 

I'll put the rootfs on NAND and try to retest. Maybe to do some other tests
in parallel to have more interrupts on the system. Will let you know if I can
reproduce the bug on sama5d3_xplained.

Cheers,
ta

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