linux-kernel - Re: [RFC,PATCH 14/14] utrace core

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Message-Id: <20091205191432.5FD8F39C46@pipsqueak.sf.frob.com>
Date:	Sat,  5 Dec 2009 11:14:32 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Ananth Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, utrace-devel@...hat.com
Subject: Re: [RFC,PATCH 14/14] utrace core

> > > +	 * Some machines get here with interrupts disabled.  The same arch
> > > +	 * code path leads to calling into get_signal_to_deliver(), which
> > > +	 * implicitly reenables them by virtue of spin_unlock_irq.
> > > +	 */
> > > +	local_irq_enable();
> >
> > Hrmm, I would much prefer to fix up the calling conventions of
> > tracehook_notify_resume() than to bury something like this in the guts
> > of a tracehook user.

The reason I did it this way was mainly just not to make the requirement
for arch maintainers' too subtle.  As it is, we just say that you call
tracehook_notify_resume() after clearing TIF_NOTIFY_RESUME, when it was
set.  That keeps the specification quite simple.  Of course, that is not
really much of a reason.  If arch folks don't mind the requirement to
replace e.g.:

	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
		clear_thread_flag(TIF_NOTIFY_RESUME);
		tracehook_notify_resume(regs);
	}

with:


	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
		local_irq_enable();
		clear_thread_flag(TIF_NOTIFY_RESUME);
		tracehook_notify_resume(regs);
	}

then that is certainly fine by me.  But we do now have almost all the
arch's calling tracehook_notify_resume() and I don't know how many of
them do it in irqs-disabled context so they would need this change.

> But in any case, imho it would be better to do this after we merge utrace,
> otherwise we need more subtle arch-dependent changes before.

I tend to agree.


Thanks,
Roland
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