linux-kernel - Re: usb/net/rt2x00: warning in rt2800_eeprom_word

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Date:   Thu, 19 Oct 2017 10:25:46 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Stanislaw Gruszka <sgruszka@...hat.com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Helmut Schaa <helmut.schaa@...glemail.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/net/rt2x00: warning in rt2800_eeprom_word_index

On Mon, Oct 16, 2017 at 2:19 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Mon, Oct 16, 2017 at 11:40 AM, Stanislaw Gruszka <sgruszka@...hat.com> wrote:
>> Hi Dmitry
>>
>> On Sat, Oct 14, 2017 at 04:38:03PM +0200, Dmitry Vyukov wrote:
>>> On Thu, Oct 12, 2017 at 9:25 AM, Stanislaw Gruszka <sgruszka@...hat.com> wrote:
>>> > Hi
>>> >
>>> > On Mon, Oct 09, 2017 at 07:50:53PM +0200, Andrey Konovalov wrote:
>>> >> I've got the following report while fuzzing the kernel with syzkaller.
>>> >>
>>> >> On commit 8a5776a5f49812d29fe4b2d0a2d71675c3facf3f (4.14-rc4).
>>> >>
>>> >> I'm not sure whether this is a bug in the driver, or just a way to
>>> >> report misbehaving device. In the latter case this shouldn't be a
>>> >> WARN() call, since WARN() means bug in the kernel.
>>> >
>>> > This is about wrong EEPROM, which reported 3 tx streams on
>>> > non 3 antenna device. I think WARN() is justified and thanks
>>> > to the call trace I was actually able to to understand what
>>> > happened.
>>> >
>>> > In general I do not think WARN() only means a kernel bug, it
>>> > can be F/W or H/W bug too.
>>>
>>> Hi Stanislaw,
>>>
>>> Printing messages is fine. Printing stacks is fine. Just please make
>>> them distinguishable from kernel bugs and don't kill the whole
>>> possibility of automated Linux kernel testing. That's an important
>>> capability.
>>
>> We do not distinguish between bugs and other problems when WARN() is
>> used in (wireless) drivers, what I think is correct, taking comment from
>> include/asm-generic/bug.h :
>>
>> /*
>>  * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
>>  * significant issues that need prompt attention if they should ever
>>  * appear at runtime.  Use the versions with printk format strings
>>  * to provide better diagnostics.
>>  */
>>
>> Historically we have BUG() to mark the bugs, but usage if it is not
>> recommended as it can kill the system, so for anything that can
>> be recovered in runtime - WARN() is recommended.
>>
>> Perhaps we can introduce another helper like PROBLEM() for marking
>> situations when something is wrong, but it is not a bug. However I'm
>> not even sure at what extent it can be used, since for many cases
>> if not the most, driver author can not tell apriori if the problem
>> is a bug in the driver or HW/FW misbehaviour (or maybe particular
>> issue can happen because of both).
>
> I will write a separate email to LKML.


Sent a mail titled "Distinguishing kernel bugs from invalid inputs" to
LKML. Here is a copy:
https://groups.google.com/forum/#!topic/syzkaller/dGh7qtbu14Q