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

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Message-ID: <CAMuHMdWAzqvh_=UEiYtCdFYvcwoRVLvO9rq8MqwCqjgSz-fm7g@mail.gmail.com>
Date:   Thu, 7 Dec 2017 08:40:07 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     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()

Hi Alan,

On Wed, Dec 6, 2017 at 11:02 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Wed, 6 Dec 2017, SF Markus Elfring wrote:
>> >>> Does the existing memory allocation error message include the
>> >>> &udev->dev device name and driver name?  If it doesn't, there will be
>> >>> no way for the user to tell that the error message is related to the
>> >>> device failure.
>> >>
>> >> No, but the effect is similar.
>> >>
>> >> OOM does a dump_stack() so this function's call tree is shown.
>> >
>> > A call stack doesn't tell you which device was being handled.
>>
>> Do you find a default Linux allocation failure report insufficient then?
>>
>> Would you like to to achieve that the requested information can be determined
>> from a backtrace?
>
> It is not practical to do this.  The memory allocation routines do not
> for what purpose the memory is being allocated; hence when a failure
> occurs they cannot tell what device (or other part of the system) will
> be affected.

If even allocation of 24 bytes fails, lots of other devices and other parts of
the system will start failing really soon...

> That's why we have a secondary error message.

... and the secondary error message would still be useless.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds