linux-kernel - Re: 2.6.24-rc8-mm1: powerpc oopses

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Message-Id: <1200617237.3839.32.camel@cinder.waste.org>
Date:	Thu, 17 Jan 2008 18:47:17 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	m.kozlowski@...land.pl, linux-kernel@...r.kernel.org,
	paulus@...ba.org, linuxppc-dev@...abs.org
Subject: Re: 2.6.24-rc8-mm1: powerpc oopses


On Thu, 2008-01-17 at 16:29 -0800, Andrew Morton wrote:
> Do we need `offset' at all?

Looks like no.

I wonder if there's a good argument for adding a pte_offset_val() which
would let us do:

pteval = pte_offset_val(pmd, addr);

and shrink the map/unmap window and overhead here and possibly
elsewhere?

Anyway, updated but still untested patch now with revealing comment:

diff -r 5595adaea70f fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c	Thu Jan 17 13:26:54 2008 -0600
+++ b/fs/proc/task_mmu.c	Thu Jan 17 18:45:57 2008 -0600
@@ -584,18 +585,19 @@
 	pte_t *pte;
 	int err = 0;
 
-	pte = pte_offset_map(pmd, addr);
-	for (; addr != end; pte++, addr += PAGE_SIZE) {
+	for (; addr != end; addr += PAGE_SIZE) {
 		u64 pfn = PM_NOT_PRESENT;
+		pte = pte_offset_map(pmd, addr);
 		if (is_swap_pte(*pte))
 			pfn = swap_pte_to_pagemap_entry(*pte);
 		else if (pte_present(*pte))
 			pfn = pte_pfn(*pte);
+		/* unmap so we're not in atomic when we copy to userspace */
+		pte_unmap(pte);
 		err = add_to_pagemap(addr, pfn, pm);
 		if (err)
 			return err;
 	}
-	pte_unmap(pte - 1);
 
 	cond_resched();
 


-- 
Mathematics is the supreme nostalgia of our time.

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