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

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Date:   Tue, 13 Dec 2016 13:38:26 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     syzkaller <syzkaller@...glegroups.com>,
        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>
Subject: Re: usb/core: warning in usb_create_ep_devs/sysfs_create_dir_ns

On Tue, 13 Dec 2016, Dmitry Vyukov wrote:

> On Tue, Dec 13, 2016 at 4:52 PM, Alan Stern <stern@...land.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