linux-kernel - Re: USB: hub: Delete an error message for a failed memory allocation in usb_hub_clear_tt

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Date:   Thu, 7 Dec 2017 16:26:48 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Dan Carpenter <dan.carpenter@...cle.com>
cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        USB list <linux-usb@...r.kernel.org>,
        Joe Perches <joe@...ches.com>,
        Daniel Drake <drake@...lessm.com>,
        Dmitry Fleytman <dmitry@...nix.com>,
        Eugene Korenevsky <ekorenevsky@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Günter Röck <linux@...ck-us.net>,
        Johan Hovold <johan@...nel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Peter Chen <peter.chen@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: USB: hub: Delete an error message for a failed memory allocation
 in usb_hub_clear_tt_buffer()

On Thu, 7 Dec 2017, Dan Carpenter wrote:

> On Thu, Dec 07, 2017 at 10:12:27AM -0500, Alan Stern wrote:
> > The real problem is that the kernel development community doesn't have
> > a fixed policy on how to handle memory allocation errors.  There are
> > several possibilities:
> > 
> > 	Ignore them on the grounds that they will never happen.
> > 	(Really?  And what is the size limit above which they
> > 	might happen?)
> > 
> 
> It's pretty rare to ignore allocation failures these days.  It causes
> static checker warnings.
> 
> Sometimes it's accepted for people to ignore errors during boot but
> I hate that because how am I supposed to filter out those static checker
> warnings?  It's better to pretend that the kernel will still boot
> without essential hardware instead of wasting everyone's time who looks
> at checker output.
> 
> > 	Ignore them on the grounds that the machine will hang or
> > 	crash in the near future.  (Is this guaranteed?)
> 
> On boot sometimes yes.
> 
> > 
> > 	Treat them like other errors: try to press forward (perhaps
> > 	in a degraded mode).
> > 
> > 	Treat them like other errors: log an error message and try
> > 	to press forward.
> > 
> 
> The standard is to treat them like errors and try press forward in a
> degraded mode but don't print a message.  Checkpatch.pl complains if you
> print a warning for allocation failures.  A lot of low level functions
> handle their own messages pretty well but especially kmalloc() does.

Which brings us back to my original objection.  If an allocation 
failure has localized effects, but the low-level warning is unable to 
specify what will be affected, how is the user supposed to connect the 
effect to the cause?

Alan Stern

> 
> I also have a special static checker warning for when people do:
> 
> 	foo = alloc();
> 	BUG_ON(!foo);
> 
> People do that occasionally but fortunately it's pretty rare.  10 years
> ago that's how btrfs did error handling, but now there are only 4 of
> these still remaining in btrfs.
> 
> regards,
> dan carpenter
> 
> 
>