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Date: Tue, 13 Dec 2016 13:38:26 -0500 (EST)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Dmitry Vyukov <dvyukov@google.com>
cc: syzkaller <syzkaller@googlegroups.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kostya Serebryany <kcc@google.com>
Subject: Re: usb/core: warning in usb_create_ep_devs/sysfs_create_dir_ns
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On Tue, 13 Dec 2016, Dmitry Vyukov wrote:

> On Tue, Dec 13, 2016 at 4:52 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > On Tue, 13 Dec 2016, Dmitry Vyukov wrote:
> >
> >> >> >  If it is
> >> >> > not a bug in kernel source code, then it must not produce a WARNING.
> >> >
> >> > What about a memory allocation failure?  The memory management part of
> >> > the kernel produces a WARNING message if an allocation fails and the
> >> > caller did not specify __GFP_NOWARN.
> >> >
> >> > There is no way for a driver to guarantee that a memory allocation
> >> > request will succeed -- failure is always an option.  But obviously
> >> > memory allocation failures are not bugs in the kernel.
> >> >
> >> > Are you saying that mm/page_alloc.c:warn_alloc() should produce
> >> > something other than a WARNING?
> >>
> >>
> >> The main thing I am saying is that we absolutely need a way for a
> >> human or a computer program to be able to determine if there is
> >> anything wrong with kernel or not.
> > Doesn't it also produce a WARNING under other circumstances?
> 
> No.
> 
> OOM is not a WARNING and is easily distinguishable from BUG/WARNING.

> Memory allocator does not print WARNINGs on allocation failures.

Do you count dev_warn the same as WARN or WARN_ON?  What about dev_WARN
or pr_warn() or printk(KERN_WARNING...)?  Maybe we're not talking about
the same messages.

The USB subsystem has got tons of dev_warn() and dev_err() calls.  
Relatively few (if any) of them are for kernel bugs.

Alan Stern