logfs: update page reference count for pined pages

LogFS sets PG_private flag to indicate a pined page. We assumed that
marking a page as private is enough to ensure its existence. But
instead it is necessary to hold a reference count to the page.

The change resolves the following BUG

BUG: Bad page state in process flush-253:16  pfn:6a6d0
page flags: 0x100000000000808(uptodate|private)

Suggested-and-Acked-by: Joern Engel <joern@logfs.org>
Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>

2 files changed, 51 insertions, 15 deletions

diff --git a/fs/logfs/readwrite.c b/fs/logfs/readwrite.c
index 2ac4217b7901..6d663e8ea6da 100644
--- a/fs/logfs/readwrite.c
+++ b/fs/logfs/readwrite.c
@@ -560,8 +560,13 @@ static void inode_free_block(struct super_block *sb, struct logfs_block *block)
 static void indirect_free_block(struct super_block *sb,
                 struct logfs_block *block)
 {
-        ClearPagePrivate(block->page);
-        block->page->private = 0;
+        struct page *page = block->page;
+
+        if (PagePrivate(page)) {
+                ClearPagePrivate(page);
+                page_cache_release(page);
+                set_page_private(page, 0);
+        }
         __free_block(sb, block);
 }
 
@@ -650,8 +655,11 @@ static void alloc_data_block(struct inode *inode, struct page *page)
         logfs_unpack_index(page->index, &bix, &level);
         block = __alloc_block(inode->i_sb, inode->i_ino, bix, level);
         block->page = page;
+
         SetPagePrivate(page);
-        page->private = (unsigned long)block;
+        page_cache_get(page);
+        set_page_private(page, (unsigned long) block);
+
         block->ops = &indirect_block_ops;
 }
 
@@ -1901,8 +1909,11 @@ static void move_page_to_inode(struct inode *inode, struct page *page)
         li->li_block = block;
 
         block->page = NULL;
-        page->private = 0;
-        ClearPagePrivate(page);
+        if (PagePrivate(page)) {
+                ClearPagePrivate(page);
+                page_cache_release(page);
+                set_page_private(page, 0);
+        }
 }
 
 static void move_inode_to_page(struct page *page, struct inode *inode)
@@ -1918,8 +1929,12 @@ static void move_inode_to_page(struct page *page, struct inode *inode)
         BUG_ON(PagePrivate(page));
         block->ops = &indirect_block_ops;
         block->page = page;
-        page->private = (unsigned long)block;
-        SetPagePrivate(page);
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                page_cache_get(page);
+                set_page_private(page, (unsigned long) block);
+        }
 
         block->inode = NULL;
         li->li_block = NULL;
diff --git a/fs/logfs/segment.c b/fs/logfs/segment.c
index 9d5187353255..6aee6092860d 100644
--- a/fs/logfs/segment.c
+++ b/fs/logfs/segment.c
@@ -86,7 +86,11 @@ int __logfs_buf_write(struct logfs_area *area, u64 ofs, void *buf, size_t len,
                 BUG_ON(!page); /* FIXME: reserve a pool */
                 SetPageUptodate(page);
                 memcpy(page_address(page) + offset, buf, copylen);
-                SetPagePrivate(page);
+
+                if (!PagePrivate(page)) {
+                        SetPagePrivate(page);
+                        page_cache_get(page);
+                }
                 page_cache_release(page);
 
                 buf += copylen;
@@ -110,7 +114,10 @@ static void pad_partial_page(struct logfs_area *area)
                 page = get_mapping_page(sb, index, 0);
                 BUG_ON(!page); /* FIXME: reserve a pool */
                 memset(page_address(page) + offset, 0xff, len);
-                SetPagePrivate(page);
+                if (!PagePrivate(page)) {
+                        SetPagePrivate(page);
+                        page_cache_get(page);
+                }
                 page_cache_release(page);
         }
 }
@@ -130,7 +137,10 @@ static void pad_full_pages(struct logfs_area *area)
                 BUG_ON(!page); /* FIXME: reserve a pool */
                 SetPageUptodate(page);
                 memset(page_address(page), 0xff, PAGE_CACHE_SIZE);
-                SetPagePrivate(page);
+                if (!PagePrivate(page)) {
+                        SetPagePrivate(page);
+                        page_cache_get(page);
+                }
                 page_cache_release(page);
                 index++;
                 no_indizes--;
@@ -485,8 +495,12 @@ static void move_btree_to_page(struct inode *inode, struct page *page,
                 mempool_free(item, super->s_alias_pool);
         }
         block->page = page;
-        SetPagePrivate(page);
-        page->private = (unsigned long)block;
+
+        if (!PagePrivate(page)) {
+                SetPagePrivate(page);
+                page_cache_get(page);
+                set_page_private(page, (unsigned long) block);
+        }
         block->ops = &indirect_block_ops;
         initialize_block_counters(page, block, data, 0);
 }
@@ -536,8 +550,12 @@ void move_page_to_btree(struct page *page)
                 list_add(&item->list, &block->item_list);
         }
         block->page = NULL;
-        ClearPagePrivate(page);
-        page->private = 0;
+
+        if (PagePrivate(page)) {
+                ClearPagePrivate(page);
+                page_cache_release(page);
+                set_page_private(page, 0);
+        }
         block->ops = &btree_block_ops;
         err = alias_tree_insert(block->sb, block->ino, block->bix, block->level,
                         block);
@@ -702,7 +720,10 @@ void freeseg(struct super_block *sb, u32 segno)
                 page = find_get_page(mapping, ofs >> PAGE_SHIFT);
                 if (!page)
                         continue;
-                ClearPagePrivate(page);
+                if (PagePrivate(page)) {
+                        ClearPagePrivate(page);
+                        page_cache_release(page);
+                }
                 page_cache_release(page);
         }
 }