linux-kernel - Re: [PATCH] i386 - Fix regression, endless loop in ptrace singlestep over an int80

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Date:	Mon, 02 Jul 2007 14:07:04 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jason Wessel <jason.wessel@...driver.com>
CC:	lkml <linux-kernel@...r.kernel.org>, stable@...nel.org,
	Chuck Ebbert <76306.1226@...puserve.com>
Subject: Re: [PATCH] i386 - Fix regression, endless loop in ptrace singlestep
 over an int80

Jason Wessel wrote:
>
> Attached is a patch with a complete test case to fix the regression 
> introduced by the commit: 635cf99a80f4ebee59d70eb64bb85ce829e4591f.
>
> This patch is against kernel 2.6.21 but the fix is applicable to 
> 2.6.21 and up.  Prior to the commit that introduced the regression the 
> ltp ptrace tests would complete correctly.  I augmented the test case 
> from the original patch header to include the problem case that shows 
> up in the lpt tests.
>
> The brief summary is that the the TIF_SINGLESTEP state needs to be 
> altered on the exit path and not the entry path to a syscall, else it 
> can loop forever on the same instruction right after the syscall is 
> executed in certain cases. 

Looks reasonable to me, but what under what circumstances can 
TIF_SINGLESTEP get lost?

    J

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