linux-kernel - Re: [PATCH] scatterlist.h: Change CONFIG_DEBUG_SG for ifdef statement in sg_set

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Date:	Sun, 3 Aug 2014 01:18:45 -0400
From:	Nick Krause <xerofoify@...il.com>
To:	Mateusz Guzik <mguzik@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] scatterlist.h: Change CONFIG_DEBUG_SG for ifdef statement
 in sg_set_bf

On Sun, Aug 3, 2014 at 1:02 AM, Mateusz Guzik <mguzik@...hat.com> wrote:
> On Sun, Aug 03, 2014 at 12:31:30AM -0400, Nick Krause wrote:
>> On Sat, Aug 2, 2014 at 11:59 PM, Mateusz Guzik <mguzik@...hat.com> wrote:
>> > On Sat, Aug 02, 2014 at 10:56:13PM -0400, Nicholas Krause wrote:
>> >> This changes the ifdef statement in sg_set_bg to !CONFIG_DEBUG_SG in order
>> >> to avoid a bug with xhci dequence/enquence functions.
>> >>
>> >> Signed-off-by: Nicholas Krause <xerofoify@...il.com>
>> >> ---
>> >>  include/linux/scatterlist.h | 2 +-
>> >>  1 file changed, 1 insertion(+), 1 deletion(-)
>> >>
>> >> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
>> >> index adae88f..62de7b3 100644
>> >> --- a/include/linux/scatterlist.h
>> >> +++ b/include/linux/scatterlist.h
>> >> @@ -111,7 +111,7 @@ static inline struct page *sg_page(struct scatterlist *sg)
>> >>  static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
>> >>                             unsigned int buflen)
>> >>  {
>> >> -#ifdef CONFIG_DEBUG_SG
>> >> +#ifdef !CONFIG_DEBUG_SG
>> >>       BUG_ON(!virt_addr_valid(buf));
>> >>  #endif
>> >
>> > Have you tried compiling this? IIRC you said you would compile your
>> > stuff, what hapened to that?
>> >
>> > What exactly were you trying to achieve? Did this BUG_ON detect a
>> > problem on your system and now you are trying to silence it?
>> >
>> > The change would be wrong even if it compiled since it would just
>> > execute the assertion only when debug is disabled.
>> >
>> > --
>> > Mateusz Guzik
>> This is the mailing theme I am getting this from,[xhci] kernel BUG at
>> include/linux/scatterlist.h:115.
>> I hope this answers your question about the BUG_ON and yes I did
>> compile check it with make
>> M=include/. I also checked usb and usb net directories too.
>
> So how have you verified it tests you change? Why didn't you perform a
> full build?
>
> This is a syntax error, I suggest you read up about C preprocessor.
>
> Your change attempts to flip the condition. Now virt_addr_valid(buf) is
> tested only with debug disabled. When you enable debug it is suddenly
> not tested - definitely does not make sense.
>
> I'm assuming you are talking about https://lkml.org/lkml/2014/7/30/810
>
> If you actually read the thread you will note:
>> Looks like I either need specify valid addresses to sg_set_buf(), or
>> just make the unit test depend on !CONFIG_DEBUG_SG.
>
> 1. It is acknowleged the problem is in the caller
> 2. There is a suggestion to ensure that the UNIT TEST is not executed if
> CONFIG_DEBUG_SG  is enabled (this part was shortened to "!CONFIG_DEBUG_SG"
> but nobody claims you can use this in if/if[n]def statements)
>
> UNIT TEST as in the thingy which resulted in passing down a buffer
> failing on this BUG_ON.
>
> There is no suggestion to do anything with sg_set_buf itself.
>
> You were advised several times to find a simpler project. Also people
> noted that a "beginner kernel programmer" actually means "seasoned
> programmer learning the kernel". It is clear you are not a seasoned
> programmer, so why do you insist on doing kernel work?
>
> I can only recommend you play with userspace programs for now. These are
> much easier to debug and experiment with, not to mention have a lot lower
> entry point.
>
> --
> Mateusz Guzik
Mateusz,
I am really losing my temper with people , when all you do is tell me to work on
something else and don't even point me to how to build test in the kernel tree.
Are you stating that your every fucking change I have to build the kernel over
again, that is  a waste of time and you known it. Please stop telling me I can
do this due to a few mistakes that you and the other developers are fucking
over doing.
Regards Nick
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