linux-kernel - Re: [RFC Patch 6/9] Use virtual debug registers in process/thread handling code

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Date:	Fri, 17 Oct 2008 17:08:29 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	prasad@...ux.vnet.ibm.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <mingo@...e.hu>,
	<jason.wessel@...driver.com>, <avi@...ranet.com>,
	<richardj_moore@...ibm.com>
Subject: Re: [RFC Patch 6/9] Use virtual debug registers in process/thread
 handling code

> There's a problem with moving the switch_to_thread_hw_breakpoint() call 
> before current is updated. [...]

I got this.  I'm just saying let's look for ways to do this better.

Hmm.  The 64-bit version of __switch_to does the current change much
earlier, before __switch_to_xtra and math_state_restore.  I wonder if the
32-bit version could change to match.  I can't see what in __switch_to_xtra
would care either way, though I may be overlooking something.  Ingo?

If this does not change, then __switch_to_xtra can pass prev,next to
switch_hw_breakpoint.  You can always do some slightly different
bookkeeping in there to know that prev->next is the switch happening,
so if there is a hit when current still == prev you can filter it out.

Thanks,
Roland
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