linux-kernel - Re: usb/core: warning in usb_create_ep_devs/sysfs_create_dir

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Date:   Mon, 12 Dec 2016 22:16:50 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: usb/core: warning in usb_create_ep_devs/sysfs_create_dir_ns

On Mon, Dec 12, 2016 at 10:05 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 12 Dec 2016, Andrey Konovalov wrote:
>
>> Hi!
>>
>> While running the syzkaller fuzzer I've got the following error report.
>>
>> On commit 3c49de52d5647cda8b42c4255cf8a29d1e22eff5 (Dev 2).
>>
>> WARNING: CPU: 2 PID: 865 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x8a/0xa0
>> gadgetfs: disconnected
>> sysfs: cannot create duplicate filename
>> '/devices/platform/dummy_hcd.0/usb2/2-1/2-1:64.0/ep_05'
>> Kernel panic - not syncing: panic_on_warn set ...
>
> I suppose we could check for USB devices that claim to have two
> endpoints with the same address.  But is it really worthwhile?  A
> kernel warning isn't so bad when you're dealing with buggy device
> firmware.

We need a clear distinction between what is a bug in kernel source
code and what is incorrect user-space code. Otherwise no automated
testing is possible. WARNING means bug in kernel source code. If it is
not a bug in kernel source code, then it must not produce a WARNING.
If it's a condition that we absolutely need to make user-space aware
of, then we can print a single line with an explanation to console
(but not prefixed with "WARNING:" nor "BUG:").