ext4: Fix mmap/truncate race when blocksize < pagesize && !nodellaoc

This patch fixes the mmap/truncate race that was fixed for delayed
allocation by merging ext4_{journalled,normal,da}_writepage() into
ext4_writepage().

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 57 insertions, 177 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 1275f34589c..97c48b5b057 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -47,6 +47,10 @@
 
 #define MPAGE_DA_EXTENT_TAIL 0x01
 
+static int __ext4_journalled_writepage(struct page *page,
+                                       struct writeback_control *wbc,
+                                       unsigned int len);
+
 static inline int ext4_begin_ordered_truncate(struct inode *inode,
                                               loff_t new_size)
 {
@@ -2392,7 +2396,7 @@ static int __mpage_da_writepage(struct page *page,
                          * We need to try to allocate
                          * unmapped blocks in the same page.
                          * Otherwise we won't make progress
-                         * with the page in ext4_da_writepage
+                         * with the page in ext4_writepage
                          */
                         if (ext4_bh_delay_or_unwritten(NULL, bh)) {
                                 mpage_add_bh_to_extent(mpd, logical,
@@ -2519,13 +2523,47 @@ static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
 }
 
 /*
+ * Note that we don't need to start a transaction unless we're journaling data
+ * because we should have holes filled from ext4_page_mkwrite(). We even don't
+ * need to file the inode to the transaction's list in ordered mode because if
+ * we are writing back data added by write(), the inode is already there and if
+ * we are writing back data modified via mmap(), noone guarantees in which
+ * transaction the data will hit the disk. In case we are journaling data, we
+ * cannot start transaction directly because transaction start ranks above page
+ * lock so we have to do some magic.
+ *
  * This function can get called via...
  *   - ext4_da_writepages after taking page lock (have journal handle)
  *   - journal_submit_inode_data_buffers (no journal handle)
  *   - shrink_page_list via pdflush (no journal handle)
  *   - grab_page_cache when doing write_begin (have journal handle)
+ *
+ * We don't do any block allocation in this function. If we have page with
+ * multiple blocks we need to write those buffer_heads that are mapped. This
+ * is important for mmaped based write. So if we do with blocksize 1K
+ * truncate(f, 1024);
+ * a = mmap(f, 0, 4096);
+ * a[0] = 'a';
+ * truncate(f, 4096);
+ * we have in the page first buffer_head mapped via page_mkwrite call back
+ * but other bufer_heads would be unmapped but dirty(dirty done via the
+ * do_wp_page). So writepage should write the first block. If we modify
+ * the mmap area beyond 1024 we will again get a page_fault and the
+ * page_mkwrite callback will do the block allocation and mark the
+ * buffer_heads mapped.
+ *
+ * We redirty the page if we have any buffer_heads that is either delay or
+ * unwritten in the page.
+ *
+ * We can get recursively called as show below.
+ *
+ *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
+ *              ext4_writepage()
+ *
+ * But since we don't do any block allocation we should not deadlock.
+ * Page also have the dirty flag cleared so we don't get recurive page_lock.
  */
-static int ext4_da_writepage(struct page *page,
+static int ext4_writepage(struct page *page,
                              struct writeback_control *wbc)
 {
         int ret = 0;
@@ -2534,7 +2572,7 @@ static int ext4_da_writepage(struct page *page,
         struct buffer_head *page_bufs;
         struct inode *inode = page->mapping->host;
 
-        trace_ext4_da_writepage(inode, page);
+        trace_ext4_writepage(inode, page);
         size = i_size_read(inode);
         if (page->index == size >> PAGE_CACHE_SHIFT)
                 len = size & ~PAGE_CACHE_MASK;
@@ -2596,6 +2634,15 @@ static int ext4_da_writepage(struct page *page,
                 block_commit_write(page, 0, len);
         }
 
+        if (PageChecked(page) && ext4_should_journal_data(inode)) {
+                /*
+                 * It's mmapped pagecache.  Add buffers and journal it.  There
+                 * doesn't seem much point in redirtying the page here.
+                 */
+                ClearPageChecked(page);
+                return __ext4_journalled_writepage(page, wbc, len);
+        }
+
         if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
                 ret = nobh_writepage(page, noalloc_get_block_write, wbc);
         else
@@ -3135,112 +3182,10 @@ static int bput_one(handle_t *handle, struct buffer_head *bh)
         return 0;
 }
 
-/*
- * Note that we don't need to start a transaction unless we're journaling data
- * because we should have holes filled from ext4_page_mkwrite(). We even don't
- * need to file the inode to the transaction's list in ordered mode because if
- * we are writing back data added by write(), the inode is already there and if
- * we are writing back data modified via mmap(), noone guarantees in which
- * transaction the data will hit the disk. In case we are journaling data, we
- * cannot start transaction directly because transaction start ranks above page
- * lock so we have to do some magic.
- *
- * In all journaling modes block_write_full_page() will start the I/O.
- *
- * Problem:
- *
- *      ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
- *              ext4_writepage()
- *
- * Similar for:
- *
- *      ext4_file_write() -> generic_file_write() -> __alloc_pages() -> ...
- *
- * Same applies to ext4_get_block().  We will deadlock on various things like
- * lock_journal and i_data_sem
- *
- * Setting PF_MEMALLOC here doesn't work - too many internal memory
- * allocations fail.
- *
- * 16May01: If we're reentered then journal_current_handle() will be
- *          non-zero. We simply *return*.
- *
- * 1 July 2001: @@@ FIXME:
- *   In journalled data mode, a data buffer may be metadata against the
- *   current transaction.  But the same file is part of a shared mapping
- *   and someone does a writepage() on it.
- *
- *   We will move the buffer onto the async_data list, but *after* it has
- *   been dirtied. So there's a small window where we have dirty data on
- *   BJ_Metadata.
- *
- *   Note that this only applies to the last partial page in the file.  The
- *   bit which block_write_full_page() uses prepare/commit for.  (That's
- *   broken code anyway: it's wrong for msync()).
- *
- *   It's a rare case: affects the final partial page, for journalled data
- *   where the file is subject to bith write() and writepage() in the same
- *   transction.  To fix it we'll need a custom block_write_full_page().
- *   We'll probably need that anyway for journalling writepage() output.
- *
- * We don't honour synchronous mounts for writepage().  That would be
- * disastrous.  Any write() or metadata operation will sync the fs for
- * us.
- *
- */
-static int __ext4_normal_writepage(struct page *page,
-                                   struct writeback_control *wbc)
-{
-        struct inode *inode = page->mapping->host;
-
-        if (test_opt(inode->i_sb, NOBH))
-                return nobh_writepage(page, noalloc_get_block_write, wbc);
-        else
-                return block_write_full_page(page, noalloc_get_block_write,
-                                             wbc);
-}
-
-static int ext4_normal_writepage(struct page *page,
-                                 struct writeback_control *wbc)
-{
-        struct inode *inode = page->mapping->host;
-        loff_t size = i_size_read(inode);
-        loff_t len;
-
-        trace_ext4_normal_writepage(inode, page);
-        J_ASSERT(PageLocked(page));
-        if (page->index == size >> PAGE_CACHE_SHIFT)
-                len = size & ~PAGE_CACHE_MASK;
-        else
-                len = PAGE_CACHE_SIZE;
-
-        if (page_has_buffers(page)) {
-                /* if page has buffers it should all be mapped
-                 * and allocated. If there are not buffers attached
-                 * to the page we know the page is dirty but it lost
-                 * buffers. That means that at some moment in time
-                 * after write_begin() / write_end() has been called
-                 * all buffers have been clean and thus they must have been
-                 * written at least once. So they are all mapped and we can
-                 * happily proceed with mapping them and writing the page.
-                 */
-                BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
-                                        ext4_bh_delay_or_unwritten));
-        }
-
-        if (!ext4_journal_current_handle())
-                return __ext4_normal_writepage(page, wbc);
-
-        redirty_page_for_writepage(wbc, page);
-        unlock_page(page);
-        return 0;
-}
-
 static int __ext4_journalled_writepage(struct page *page,
-                                       struct writeback_control *wbc)
+                                       struct writeback_control *wbc,
+                                       unsigned int len)
 {
-        loff_t size;
-        unsigned int len;
         struct address_space *mapping = page->mapping;
         struct inode *inode = mapping->host;
         struct buffer_head *page_bufs;
@@ -3248,16 +3193,8 @@ static int __ext4_journalled_writepage(struct page *page,
         int ret = 0;
         int err;
 
-        size = i_size_read(inode);
-        if (page->index == size >> PAGE_CACHE_SHIFT)
-                len = size & ~PAGE_CACHE_MASK;
-        else
-                len = PAGE_CACHE_SIZE;
-        ret = block_prepare_write(page, 0, len, noalloc_get_block_write);
-        if (ret != 0)
-                goto out_unlock;
-
         page_bufs = page_buffers(page);
+        BUG_ON(!page_bufs);
         walk_page_buffers(handle, page_bufs, 0, len, NULL, bget_one);
         /* As soon as we unlock the page, it can go away, but we have
          * references to buffers so we are safe */
@@ -3282,67 +3219,10 @@ static int __ext4_journalled_writepage(struct page *page,
 
         walk_page_buffers(handle, page_bufs, 0, len, NULL, bput_one);
         EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
-        goto out;
-
-out_unlock:
-        unlock_page(page);
 out:
         return ret;
 }
 
-static int ext4_journalled_writepage(struct page *page,
-                                     struct writeback_control *wbc)
-{
-        struct inode *inode = page->mapping->host;
-        loff_t size = i_size_read(inode);
-        loff_t len;
-
-        trace_ext4_journalled_writepage(inode, page);
-        J_ASSERT(PageLocked(page));
-        if (page->index == size >> PAGE_CACHE_SHIFT)
-                len = size & ~PAGE_CACHE_MASK;
-        else
-                len = PAGE_CACHE_SIZE;
-
-        if (page_has_buffers(page)) {
-                /* if page has buffers it should all be mapped
-                 * and allocated. If there are not buffers attached
-                 * to the page we know the page is dirty but it lost
-                 * buffers. That means that at some moment in time
-                 * after write_begin() / write_end() has been called
-                 * all buffers have been clean and thus they must have been
-                 * written at least once. So they are all mapped and we can
-                 * happily proceed with mapping them and writing the page.
-                 */
-                BUG_ON(walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
-                                        ext4_bh_delay_or_unwritten));
-        }
-
-        if (ext4_journal_current_handle())
-                goto no_write;
-
-        if (PageChecked(page)) {
-                /*
-                 * It's mmapped pagecache.  Add buffers and journal it.  There
-                 * doesn't seem much point in redirtying the page here.
-                 */
-                ClearPageChecked(page);
-                return __ext4_journalled_writepage(page, wbc);
-        } else {
-                /*
-                 * It may be a page full of checkpoint-mode buffers.  We don't
-                 * really know unless we go poke around in the buffer_heads.
-                 * But block_write_full_page will do the right thing.
-                 */
-                return block_write_full_page(page, noalloc_get_block_write,
-                                             wbc);
-        }
-no_write:
-        redirty_page_for_writepage(wbc, page);
-        unlock_page(page);
-        return 0;
-}
-
 static int ext4_readpage(struct file *file, struct page *page)
 {
         return mpage_readpage(page, ext4_get_block);
@@ -3489,7 +3369,7 @@ static int ext4_journalled_set_page_dirty(struct page *page)
 static const struct address_space_operations ext4_ordered_aops = {
         .readpage               = ext4_readpage,
         .readpages              = ext4_readpages,
-        .writepage              = ext4_normal_writepage,
+        .writepage              = ext4_writepage,
         .sync_page              = block_sync_page,
         .write_begin            = ext4_write_begin,
         .write_end              = ext4_ordered_write_end,
@@ -3504,7 +3384,7 @@ static const struct address_space_operations ext4_ordered_aops = {
 static const struct address_space_operations ext4_writeback_aops = {
         .readpage               = ext4_readpage,
         .readpages              = ext4_readpages,
-        .writepage              = ext4_normal_writepage,
+        .writepage              = ext4_writepage,
         .sync_page              = block_sync_page,
         .write_begin            = ext4_write_begin,
         .write_end              = ext4_writeback_write_end,
@@ -3519,7 +3399,7 @@ static const struct address_space_operations ext4_writeback_aops = {
 static const struct address_space_operations ext4_journalled_aops = {
         .readpage               = ext4_readpage,
         .readpages              = ext4_readpages,
-        .writepage              = ext4_journalled_writepage,
+        .writepage              = ext4_writepage,
         .sync_page              = block_sync_page,
         .write_begin            = ext4_write_begin,
         .write_end              = ext4_journalled_write_end,
@@ -3533,7 +3413,7 @@ static const struct address_space_operations ext4_journalled_aops = {
 static const struct address_space_operations ext4_da_aops = {
         .readpage               = ext4_readpage,
         .readpages              = ext4_readpages,
-        .writepage              = ext4_da_writepage,
+        .writepage              = ext4_writepage,
         .writepages             = ext4_da_writepages,
         .sync_page              = block_sync_page,
         .write_begin            = ext4_da_write_begin,