1 files changed, 58 insertions, 135 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 4ce02e0..bd10636 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -264,46 +264,55 @@ static int shmem_radix_tree_replace(struct address_space *mapping,
 }
 
 /*
+ * Sometimes, before we decide whether to proceed or to fail, we must check
+ * that an entry was not already brought back from swap by a racing thread.
+ *
+ * Checking page is not enough: by the time a SwapCache page is locked, it
+ * might be reused, and again be SwapCache, using the same swap as before.
+ */
+static bool shmem_confirm_swap(struct address_space *mapping,
+			       pgoff_t index, swp_entry_t swap)
+{
+	void *item;
+
+	rcu_read_lock();
+	item = radix_tree_lookup(&mapping->page_tree, index);
+	rcu_read_unlock();
+	return item == swp_to_radix_entry(swap);
+}
+
+/*
  * Like add_to_page_cache_locked, but error if expected item has gone.
  */
 static int shmem_add_to_page_cache(struct page *page,
 				   struct address_space *mapping,
 				   pgoff_t index, gfp_t gfp, void *expected)
 {
-	int error = 0;
+	int error;
 
 	VM_BUG_ON(!PageLocked(page));
 	VM_BUG_ON(!PageSwapBacked(page));
 
+	page_cache_get(page);
+	page->mapping = mapping;
+	page->index = index;
+
+	spin_lock_irq(&mapping->tree_lock);
 	if (!expected)
-		error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+		error = radix_tree_insert(&mapping->page_tree, index, page);
+	else
+		error = shmem_radix_tree_replace(mapping, index, expected,
+								 page);
 	if (!error) {
-		page_cache_get(page);
-		page->mapping = mapping;
-		page->index = index;
-
-		spin_lock_irq(&mapping->tree_lock);
-		if (!expected)
-			error = radix_tree_insert(&mapping->page_tree,
-							index, page);
-		else
-			error = shmem_radix_tree_replace(mapping, index,
-							expected, page);
-		if (!error) {
-			mapping->nrpages++;
-			__inc_zone_page_state(page, NR_FILE_PAGES);
-			__inc_zone_page_state(page, NR_SHMEM);
-			spin_unlock_irq(&mapping->tree_lock);
-		} else {
-			page->mapping = NULL;
-			spin_unlock_irq(&mapping->tree_lock);
-			page_cache_release(page);
-		}
-		if (!expected)
-			radix_tree_preload_end();
+		mapping->nrpages++;
+		__inc_zone_page_state(page, NR_FILE_PAGES);
+		__inc_zone_page_state(page, NR_SHMEM);
+		spin_unlock_irq(&mapping->tree_lock);
+	} else {
+		page->mapping = NULL;
+		spin_unlock_irq(&mapping->tree_lock);
+		page_cache_release(page);
 	}
-	if (error)
-		mem_cgroup_uncharge_cache_page(page);
 	return error;
 }
 
@@ -1124,9 +1133,9 @@ repeat:
 		/* We have to do this with page locked to prevent races */
 		lock_page(page);
 		if (!PageSwapCache(page) || page_private(page) != swap.val ||
-		    page->mapping) {
+		    !shmem_confirm_swap(mapping, index, swap)) {
 			error = -EEXIST;	/* try again */
-			goto failed;
+			goto unlock;
 		}
 		if (!PageUptodate(page)) {
 			error = -EIO;
@@ -1142,9 +1151,12 @@ repeat:
 
 		error = mem_cgroup_cache_charge(page, current->mm,
 						gfp & GFP_RECLAIM_MASK);
-		if (!error)
+		if (!error) {
 			error = shmem_add_to_page_cache(page, mapping, index,
 						gfp, swp_to_radix_entry(swap));
+			/* We already confirmed swap, and make no allocation */
+			VM_BUG_ON(error);
+		}
 		if (error)
 			goto failed;
 
@@ -1181,11 +1193,18 @@ repeat:
 		__set_page_locked(page);
 		error = mem_cgroup_cache_charge(page, current->mm,
 						gfp & GFP_RECLAIM_MASK);
-		if (!error)
-			error = shmem_add_to_page_cache(page, mapping, index,
-						gfp, NULL);
 		if (error)
 			goto decused;
+		error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
+		if (!error) {
+			error = shmem_add_to_page_cache(page, mapping, index,
+							gfp, NULL);
+			radix_tree_preload_end();
+		}
+		if (error) {
+			mem_cgroup_uncharge_cache_page(page);
+			goto decused;
+		}
 		lru_cache_add_anon(page);
 
 		spin_lock(&info->lock);
@@ -1245,14 +1264,10 @@ decused:
 unacct:
 	shmem_unacct_blocks(info->flags, 1);
 failed:
-	if (swap.val && error != -EINVAL) {
-		struct page *test = find_get_page(mapping, index);
-		if (test && !radix_tree_exceptional_entry(test))
-			page_cache_release(test);
-		/* Have another try if the entry has changed */
-		if (test != swp_to_radix_entry(swap))
-			error = -EEXIST;
-	}
+	if (swap.val && error != -EINVAL &&
+	    !shmem_confirm_swap(mapping, index, swap))
+		error = -EEXIST;
+unlock:
 	if (page) {
 		unlock_page(page);
 		page_cache_release(page);
@@ -1264,7 +1279,7 @@ failed:
 		spin_unlock(&info->lock);
 		goto repeat;
 	}
-	if (error == -EEXIST)
+	if (error == -EEXIST)	/* from above or from radix_tree_insert */
 		goto repeat;
 	return error;
 }
@@ -1692,98 +1707,6 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
 	return error;
 }
 
-/*
- * llseek SEEK_DATA or SEEK_HOLE through the radix_tree.
- */
-static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
-				    pgoff_t index, pgoff_t end, int origin)
-{
-	struct page *page;
-	struct pagevec pvec;
-	pgoff_t indices[PAGEVEC_SIZE];
-	bool done = false;
-	int i;
-
-	pagevec_init(&pvec, 0);
-	pvec.nr = 1;		/* start small: we may be there already */
-	while (!done) {
-		pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
-					pvec.nr, pvec.pages, indices);
-		if (!pvec.nr) {
-			if (origin == SEEK_DATA)
-				index = end;
-			break;
-		}
-		for (i = 0; i < pvec.nr; i++, index++) {
-			if (index < indices[i]) {
-				if (origin == SEEK_HOLE) {
-					done = true;
-					break;
-				}
-				index = indices[i];
-			}
-			page = pvec.pages[i];
-			if (page && !radix_tree_exceptional_entry(page)) {
-				if (!PageUptodate(page))
-					page = NULL;
-			}
-			if (index >= end ||
-			    (page && origin == SEEK_DATA) ||
-			    (!page && origin == SEEK_HOLE)) {
-				done = true;
-				break;
-			}
-		}
-		shmem_deswap_pagevec(&pvec);
-		pagevec_release(&pvec);
-		pvec.nr = PAGEVEC_SIZE;
-		cond_resched();
-	}
-	return index;
-}
-
-static loff_t shmem_file_llseek(struct file *file, loff_t offset, int origin)
-{
-	struct address_space *mapping;
-	struct inode *inode;
-	pgoff_t start, end;
-	loff_t new_offset;
-
-	if (origin != SEEK_DATA && origin != SEEK_HOLE)
-		return generic_file_llseek_size(file, offset, origin,
-							MAX_LFS_FILESIZE);
-	mapping = file->f_mapping;
-	inode = mapping->host;
-	mutex_lock(&inode->i_mutex);
-	/* We're holding i_mutex so we can access i_size directly */
-
-	if (offset < 0)
-		offset = -EINVAL;
-	else if (offset >= inode->i_size)
-		offset = -ENXIO;
-	else {
-		start = offset >> PAGE_CACHE_SHIFT;
-		end = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-		new_offset = shmem_seek_hole_data(mapping, start, end, origin);
-		new_offset <<= PAGE_CACHE_SHIFT;
-		if (new_offset > offset) {
-			if (new_offset < inode->i_size)
-				offset = new_offset;
-			else if (origin == SEEK_DATA)
-				offset = -ENXIO;
-			else
-				offset = inode->i_size;
-		}
-	}
-
-	if (offset >= 0 && offset != file->f_pos) {
-		file->f_pos = offset;
-		file->f_version = 0;
-	}
-	mutex_unlock(&inode->i_mutex);
-	return offset;
-}
-
 static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 							 loff_t len)
 {
@@ -2787,7 +2710,7 @@ static const struct address_space_operations shmem_aops = {
 static const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
 #ifdef CONFIG_TMPFS
-	.llseek		= shmem_file_llseek,
+	.llseek		= generic_file_llseek,
 	.read		= do_sync_read,
 	.write		= do_sync_write,
 	.aio_read	= shmem_file_aio_read,