linux-kernel - Re: s390 && user_enable_single_step() (Was: odd utrace testing results on s390x)

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Message-Id: <20100106211536.0F6AC134D@magilla.sf.frob.com>
Date:	Wed,  6 Jan 2010 13:15:36 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, caiqian@...hat.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jan Kratochvil <jkratoch@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	utrace-devel@...hat.com
Subject: Re: s390 && user_enable_single_step() (Was: odd utrace testing
 results on s390x)

> > then the test-case from 6580807da14c423f0d0a708108e6df6ebc8bc83d
> > fails. This probably means that copy_process()->user_disable_single_step()
> > is not enough to clear the "this task wants single-stepping" copied
> > from parent.
> 
> user_disable_single_step() does not remove the TIF_SINGLE_STEP bit from the
> forked task. Perhaps we should just clear the bit in the function.

If that were to fix this test case, I think it would be incidental rather
than meaning the right thing.  The "this task wants single-stepping" state
should not have anything to do with TIF_SINGLE_STEP.  It means "this task
recently had single-stepping", which is a separate moving part.

Thanks,
Roland
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