linux-kernel - [PATCH 3/3] mm: Cause revoke_mappings to wait until all close methods have completed.

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Date:	Sat, 25 Sep 2010 16:34:51 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hugh@...itas.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, Rik van Riel <riel@...hat.com>
Subject: [PATCH 3/3] mm: Cause revoke_mappings to wait until all close methods have completed.


Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
---
 include/linux/fs.h |    2 ++
 mm/mmap.c          |   13 ++++++++++++-
 mm/revoke.c        |   18 +++++++++++++++---
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 76041b6..5d3d6b8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -633,6 +633,8 @@ struct address_space {
 	const struct address_space_operations *a_ops;	/* methods */
 	unsigned long		flags;		/* error bits/gfp mask */
 	struct backing_dev_info *backing_dev_info; /* device readahead, etc */
+	struct task_struct	*revoke_task;	/* Who to wake up when all vmas are closed */
+	unsigned int		close_count;	/* Cover race conditions with revoke_mappings */
 	spinlock_t		private_lock;	/* for use by the address_space */
 	struct list_head	private_list;	/* ditto */
 	struct address_space	*assoc_mapping;	/* ditto */
diff --git a/mm/mmap.c b/mm/mmap.c
index 17dd003..3df3193 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -218,6 +218,7 @@ void unlink_file_vma(struct vm_area_struct *vma)
 		struct address_space *mapping = file->f_mapping;
 		spin_lock(&mapping->i_mmap_lock);
 		__remove_shared_vm_struct(vma, file, mapping);
+		mapping->close_count++;
 		spin_unlock(&mapping->i_mmap_lock);
 	}
 }
@@ -233,9 +234,19 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
 	if (vma->vm_ops && vma->vm_ops->close)
 		vma->vm_ops->close(vma);
 	if (vma->vm_file) {
-		fput(vma->vm_file);
+		struct address_space *mapping = vma->vm_file->f_mapping;
 		if (vma->vm_flags & VM_EXECUTABLE)
 			removed_exe_file_vma(vma->vm_mm);
+
+		/* Decrement the close count and wake up a revoker if present */
+		spin_lock(&mapping->i_mmap_lock);
+		mapping->close_count--;
+		if ((mapping->close_count == 0) && mapping->revoke_task)
+			/* Is wake_up_process the right variant of try_to_wake_up? */
+			wake_up_process(mapping->revoke_task);
+		spin_unlock(&mapping->i_mmap_lock);
+
+		fput(vma->vm_file);
 	}
 	mpol_put(vma_policy(vma));
 	kmem_cache_free(vm_area_cachep, vma);
diff --git a/mm/revoke.c b/mm/revoke.c
index a76cd1a..e19f7df 100644
--- a/mm/revoke.c
+++ b/mm/revoke.c
@@ -143,15 +143,17 @@ void revoke_mappings(struct address_space *mapping)
 	/* Make any access to previously mapped pages trigger a SIGBUS,
 	 * and stop calling vm_ops methods.
 	 *
-	 * When revoke_mappings returns invocations of vm_ops->close
-	 * may still be in progress, but no invocations of any other
-	 * vm_ops methods will be.
+	 * When revoke_mappings no invocations of any method will be
+	 * in progress.
 	 */
 	struct vm_area_struct *vma;
 	struct prio_tree_iter iter;
 
 	spin_lock(&mapping->i_mmap_lock);
 
+	WARN_ON(mapping->revoke_task);
+	mapping->revoke_task = current;
+
 restart_tree:
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX) {
 		if (revoke_mapping(mapping, vma->vm_mm, vma->vm_start))
@@ -164,6 +166,16 @@ restart_list:
 			goto restart_list;
 	}
 
+	while (!list_empty(&mapping->i_mmap_nonlinear) ||
+	       !prio_tree_empty(&mapping->i_mmap) ||
+	       mapping->close_count)
+	{
+		__set_current_state(TASK_UNINTERRUPTIBLE);
+		spin_unlock(&mapping->i_mmap_lock);
+		schedule();
+		spin_lock(&mapping->i_mmap_lock);
+	}
+	mapping->revoke_task = NULL;
 	spin_unlock(&mapping->i_mmap_lock);
 }
 EXPORT_SYMBOL_GPL(revoke_mappings);
-- 
1.7.2.3

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