linux-kernel - [PATCH] rmap: make anon_vma_prepare link in all the anon

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Date:	Tue, 6 Apr 2010 19:54:59 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com, hannes@...xchg.org
Subject: [PATCH] rmap: make anon_vma_prepare link in all the anon_vmas of a
 mergeable VMA

When a new VMA has a mergeable anon_vma with a neighboring VMA,
make sure all of the neighbor's old anon_vma structs are also
linked in.

This is necessary because at some point the VMAs could get merged,
and we want to ensure no anon_vma structs get freed prematurely,
while the system still has anonymous pages that belong to those
structs.

Reported-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Rik van Riel <riel@...hat.com>

--- 
 include/linux/mm.h |    2 +-
 mm/mmap.c          |    6 +++---
 mm/rmap.c          |   20 +++++++++++++-------
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e70f21b..90ac50e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1228,7 +1228,7 @@ extern struct vm_area_struct *vma_merge(struct mm_struct *,
 	struct vm_area_struct *prev, unsigned long addr, unsigned long end,
 	unsigned long vm_flags, struct anon_vma *, struct file *, pgoff_t,
 	struct mempolicy *);
-extern struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *);
+extern struct vm_area_struct *find_mergeable_anon_vma(struct vm_area_struct *);
 extern int split_vma(struct mm_struct *,
 	struct vm_area_struct *, unsigned long addr, int new_below);
 extern int insert_vm_struct(struct mm_struct *, struct vm_area_struct *);
diff --git a/mm/mmap.c b/mm/mmap.c
index 75557c6..bf0600c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -832,7 +832,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
  * anon_vmas being allocated, preventing vma merge in subsequent
  * mprotect.
  */
-struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
+struct vm_area_struct *find_mergeable_anon_vma(struct vm_area_struct *vma)
 {
 	struct vm_area_struct *near;
 	unsigned long vm_flags;
@@ -855,7 +855,7 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
 			can_vma_merge_before(near, vm_flags,
 				NULL, vma->vm_file, vma->vm_pgoff +
 				((vma->vm_end - vma->vm_start) >> PAGE_SHIFT)))
-		return near->anon_vma;
+		return near;
 try_prev:
 	/*
 	 * It is potentially slow to have to call find_vma_prev here.
@@ -875,7 +875,7 @@ try_prev:
   			mpol_equal(vma_policy(near), vma_policy(vma)) &&
 			can_vma_merge_after(near, vm_flags,
 				NULL, vma->vm_file, vma->vm_pgoff))
-		return near->anon_vma;
+		return near;
 none:
 	/*
 	 * There's no absolute need to look only at touching neighbours:
diff --git a/mm/rmap.c b/mm/rmap.c
index eaa7a09..60616db 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -119,20 +119,26 @@ int anon_vma_prepare(struct vm_area_struct *vma)
 	might_sleep();
 	if (unlikely(!anon_vma)) {
 		struct mm_struct *mm = vma->vm_mm;
+		struct vm_area_struct *merge_vma;
 		struct anon_vma *allocated;
 
+		merge_vma = find_mergeable_anon_vma(vma);
+		if (merge_vma) {
+			if (anon_vma_clone(vma, merge_vma))
+				goto out_enomem;
+			return 0;
+		}
+
 		avc = anon_vma_chain_alloc();
 		if (!avc)
 			goto out_enomem;
 
-		anon_vma = find_mergeable_anon_vma(vma);
 		allocated = NULL;
-		if (!anon_vma) {
-			anon_vma = anon_vma_alloc();
-			if (unlikely(!anon_vma))
-				goto out_enomem_free_avc;
-			allocated = anon_vma;
-		}
+		anon_vma = anon_vma_alloc();
+		if (unlikely(!anon_vma))
+			goto out_enomem_free_avc;
+		allocated = anon_vma;
+
 		spin_lock(&anon_vma->lock);
 
 		/* page_table_lock to protect against threads */
--
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