linux-kernel - Re: [patch 3/5] x86: finish fault error path with fatal signal

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Date:	Thu, 25 Jul 2013 17:50:33 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Michal Hocko <mhocko@...e.cz>, azurIt <azurit@...ox.sk>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	righi.andrea@...il.com
Subject: Re: [patch 3/5] x86: finish fault error path with fatal signal

On Thu, Jul 25, 2013 at 04:29:13PM -0400, KOSAKI Motohiro wrote:
> (7/24/13 4:32 PM), Johannes Weiner wrote:
> >@@ -1189,9 +1174,17 @@ good_area:
> >  	 */
> >  	fault = handle_mm_fault(mm, vma, address, flags);
> >
> >-	if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
> >-		if (mm_fault_error(regs, error_code, address, fault))
> >-			return;
> >+	/*
> >+	 * If we need to retry but a fatal signal is pending, handle the
> >+	 * signal first. We do not need to release the mmap_sem because it
> >+	 * would already be released in __lock_page_or_retry in mm/filemap.c.
> >+	 */
> >+	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
> >+		return;
> >+
> >+	if (unlikely(fault & VM_FAULT_ERROR)) {
> >+		mm_fault_error(regs, error_code, address, fault);
> >+		return;
> >  	}
> 
> When I made the patch you removed code, Ingo suggested we need put all rare case code
> into if(unlikely()) block. Yes, this is purely micro optimization. But it is not costly
> to maintain.

Fair enough, thanks for the heads up!
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