linux-kernel - Re: [patch 2/3] mmu_notifier: Callbacks to invalidate address ranges

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Date:	Fri, 1 Feb 2008 11:13:07 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Robin Holt <holt@....com>
cc:	Andrea Arcangeli <andrea@...ranet.com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/3] mmu_notifier: Callbacks to invalidate address ranges

On Fri, 1 Feb 2008, Robin Holt wrote:

> Maybe I haven't looked closely enough, but let's start with some common
> assumptions.  Looking at do_wp_page from 2.6.24 (I believe that is what
> my work area is based upon).  On line 1559, the function begins being
> declared.

Aah I looked at the wrong file.

> On lines 1614 and 1630, we do "goto unlock" where the _end callout is
> soon made.  The _begin callout does not come until after those branches
> have been taken (occurs on line 1648).

There are actually two cases...

---
 mm/memory.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c	2008-02-01 11:04:21.000000000 -0800
+++ linux-2.6/mm/memory.c	2008-02-01 11:12:12.000000000 -0800
@@ -1611,8 +1611,10 @@ static int do_wp_page(struct mm_struct *
 			page_table = pte_offset_map_lock(mm, pmd, address,
 							 &ptl);
 			page_cache_release(old_page);
-			if (!pte_same(*page_table, orig_pte))
-				goto unlock;
+			if (!pte_same(*page_table, orig_pte)) {
+				pte_unmap_unlock(page_table, ptl);
+				goto check_dirty;
+			}
 
 			page_mkwrite = 1;
 		}
@@ -1628,7 +1630,8 @@ static int do_wp_page(struct mm_struct *
 		if (ptep_set_access_flags(vma, address, page_table, entry,1))
 			update_mmu_cache(vma, address, entry);
 		ret |= VM_FAULT_WRITE;
-		goto unlock;
+		pte_unmap_unlock(page_table, ptl);
+		goto check_dirty;
 	}
 
 	/*
@@ -1684,10 +1687,10 @@ gotten:
 		page_cache_release(new_page);
 	if (old_page)
 		page_cache_release(old_page);
-unlock:
 	pte_unmap_unlock(page_table, ptl);
 	mmu_notifier(invalidate_range_end, mm,
 				address, address + PAGE_SIZE, 0);
+check_dirty:
 	if (dirty_page) {
 		if (vma->vm_file)
 			file_update_time(vma->vm_file);
--
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