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

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Date:	Mon, 02 Jul 2007 15:53:44 -0500
From:	Jason Wessel <jason.wessel@...driver.com>
To:	lkml <linux-kernel@...r.kernel.org>, stable@...nel.org
Subject: [PATCH] i386 - Fix regression, endless loop in ptrace singlestep
 over an int80

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.

Thanks,
Jason.

View attachment "ptrace_int80_loop_fix.patch" of type "text/plain" (2872 bytes)