linux-kernel - Re: [PATCH] timekeeping fix mismerge

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Date:	Mon, 14 May 2007 12:25:02 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH] timekeeping fix mismerge

On Mon, 14 May 2007, Thomas Gleixner wrote:
>
> The time keeping code move to kernel/time/timekeeping.c broke the
> clocksource resume logic patch. Fix it up and move the
> clocksource_resume() call to the appropriate place.

Yeah, looks obvious enough. It had just enough context in the *wrong* 
place, that the patch would continue to apply if you used the default 
(insane) GNU patch semantics, because GNU patch defaults to --fuzz=2, and 
is thus ok if it can find even just a single line around the patch that is 
valid.

So it looks like Andrew's patch-application scripts happily added the 
"clocksource_resume()" to an insane place, because the one-line context 
was

>  
> +	clocksource_resume();
> +
>  	write_seqlock_irqsave(&xtime_lock, flags);

ie an empty line and a single write_seqlock_irqsave(). And those two lines 
could be found elsewhere in the wrong file.

There's a real reason I consider GNU patch defaults to be totally insane.

I personally use much stricter rules, but what happens is that Andrew's 
scripts will apply the patch to the wrong place, and then the diff gets 
*re-generated*, so by the time I see it, I see a nice diff that applies 
with no fuzz at all.

I don't think re-generating the diff is wrong, and in fact I think you 
have to do it, but I think Andrew should use "--fuzz=0" or at least 
"--fuzz=1" instead of the default 2. Yeah, it obviously causes more patch 
application failures, and it can be very irritating if *most* of those 
patches would have applied cleanly and correctly with --fuzz=2, but 
--fuzz=2 really is very dangerous. It literally just needed two lines to 
match in the wrong place (and as mentioned, those two lines can be 
trivial, like in the example - totally empty, even!)

		Linus
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