ext4: Invert lock ordering of page_lock and transaction start in delalloc

With the reverse locking, we need to start a transation before taking
the page lock, so in ext4_da_writepages() we need to break the write-out
into chunks, and restart the journal for each chunck to ensure the
write-out fits in a single transaction.

Updated patch from Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
which fixes delalloc sync hang with journal lock inversion, and address
the performance regression issue.

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

fs/ext4/extents.c

@@ -2565,6 +2565,7 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 	int err = 0, depth, ret;
 	unsigned long allocated = 0;
 	struct ext4_allocation_request ar;
+	loff_t disksize;
 
 	__clear_bit(BH_New, &bh_result->b_state);
 	ext_debug("blocks %u/%lu requested for inode %u\n",
@@ -2755,8 +2756,13 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 	newblock = ext_pblock(&newex);
 	allocated = ext4_ext_get_actual_len(&newex);
 outnew:
-	if (extend_disksize && inode->i_size > EXT4_I(inode)->i_disksize)
-		EXT4_I(inode)->i_disksize = inode->i_size;
+	if (extend_disksize) {
+		disksize = ((loff_t) iblock + ar.len) << inode->i_blkbits;
+		if (disksize > i_size_read(inode))
+			disksize = i_size_read(inode);
+		if (disksize > EXT4_I(inode)->i_disksize)
+			EXT4_I(inode)->i_disksize = disksize;
+	}
 
 	set_buffer_new(bh_result);
 

fs/ext4/inode.c

@@ -847,6 +847,7 @@ int ext4_get_blocks_handle(handle_t *handle, struct inode *inode,
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	int count = 0;
 	ext4_fsblk_t first_block = 0;
+	loff_t disksize;
 
 
 	J_ASSERT(!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL));
@@ -922,8 +923,13 @@ int ext4_get_blocks_handle(handle_t *handle, struct inode *inode,
 	 * protect it if you're about to implement concurrent
 	 * ext4_get_block() -bzzz
 	*/
-	if (!err && extend_disksize && inode->i_size > ei->i_disksize)
-		ei->i_disksize = inode->i_size;
+	if (!err && extend_disksize) {
+		disksize = ((loff_t) iblock + count) << inode->i_blkbits;
+		if (disksize > i_size_read(inode))
+			disksize = i_size_read(inode);
+		if (disksize > ei->i_disksize)
+			ei->i_disksize = disksize;
+	}
 	if (err)
 		goto cleanup;
 
@@ -1683,13 +1689,11 @@ static void mpage_put_bnr_to_bhs(struct mpage_da_data *mpd, sector_t logical,
 			do {
 				if (cur_logical >= logical + blocks)
 					break;
-
 				if (buffer_delay(bh)) {
 					bh->b_blocknr = pblock;
 					clear_buffer_delay(bh);
-				} else if (buffer_mapped(bh)) {
+				} else if (buffer_mapped(bh))
 					BUG_ON(bh->b_blocknr != pblock);
-				}
 
 				cur_logical++;
 				pblock++;
@@ -1764,10 +1768,10 @@ static void mpage_da_map_blocks(struct mpage_da_data *mpd)
 		if (buffer_delay(lbh))
 			mpage_put_bnr_to_bhs(mpd, next, &new);
 
-			/* go for the remaining blocks */
-			next += new.b_size >> mpd->inode->i_blkbits;
-			remain -= new.b_size;
-		}
+		/* go for the remaining blocks */
+		next += new.b_size >> mpd->inode->i_blkbits;
+		remain -= new.b_size;
+	}
 }
 
 #define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | (1 << BH_Delay))
@@ -1993,18 +1997,14 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
 static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
 				   struct buffer_head *bh_result, int create)
 {
-	int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
+	int ret;
 	unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
 	loff_t disksize = EXT4_I(inode)->i_disksize;
 	handle_t *handle = NULL;
 
-	if (create) {
-		handle = ext4_journal_start(inode, needed_blocks);
-		if (IS_ERR(handle)) {
-			ret = PTR_ERR(handle);
-			goto out;
-		}
-	}
+	handle = ext4_journal_current_handle();
+	BUG_ON(handle == NULL);
+	BUG_ON(create == 0);
 
 	ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
 				   bh_result, create, 0, EXT4_DELALLOC_RSVED);
@@ -2029,65 +2029,157 @@ static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
 			up_write(&EXT4_I(inode)->i_data_sem);
 
 			if (EXT4_I(inode)->i_disksize == disksize) {
-				if (handle == NULL)
-					handle = ext4_journal_start(inode, 1);
-				if (!IS_ERR(handle))
-					ext4_mark_inode_dirty(handle, inode);
+				ret = ext4_mark_inode_dirty(handle, inode);
+				return ret;
 			}
 		}
-
 		ret = 0;
 	}
-
-out:
-	if (handle && !IS_ERR(handle))
-		ext4_journal_stop(handle);
-
 	return ret;
 }
+
+static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
+{
+	return !buffer_mapped(bh) || buffer_delay(bh);
+}
+
 /* FIXME!! only support data=writeback mode */
+/*
+ * get called vi ext4_da_writepages after taking page lock
+ * We may end up doing block allocation here in case
+ * mpage_da_map_blocks failed to allocate blocks.
+ */
 static int ext4_da_writepage(struct page *page,
 				struct writeback_control *wbc)
 {
-	struct inode *inode = page->mapping->host;
-	handle_t *handle = NULL;
 	int ret = 0;
-	int err;
+	loff_t size;
+	unsigned long len;
+	handle_t *handle = NULL;
+	struct buffer_head *page_bufs;
+	struct inode *inode = page->mapping->host;
 
-	if (ext4_journal_current_handle())
-		goto out_fail;
+	handle = ext4_journal_current_handle();
+	if (!handle) {
+		/*
+		 * This can happen when we aren't called via
+		 * ext4_da_writepages() but directly (shrink_page_list).
+		 * We cannot easily start a transaction here so we just skip
+		 * writing the page in case we would have to do so.
+		 */
+		size = i_size_read(inode);
 
-	handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
-	if (IS_ERR(handle)) {
-		ret = PTR_ERR(handle);
-		goto out_fail;
+		page_bufs = page_buffers(page);
+		if (page->index == size >> PAGE_CACHE_SHIFT)
+			len = size & ~PAGE_CACHE_MASK;
+		else
+			len = PAGE_CACHE_SIZE;
+
+		if (walk_page_buffers(NULL, page_bufs, 0,
+				len, NULL, ext4_bh_unmapped_or_delay)) {
+			/*
+			 * We can't do block allocation under
+			 * page lock without a handle . So redirty
+			 * the page and return
+			 */
+			BUG_ON(wbc->sync_mode != WB_SYNC_NONE);
+			redirty_page_for_writepage(wbc, page);
+			unlock_page(page);
+			return 0;
+		}
 	}
 
 	if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
-		ret = nobh_writepage(page, ext4_get_block, wbc);
+		ret = nobh_writepage(page, ext4_da_get_block_write, wbc);
 	else
-		ret = block_write_full_page(page, ext4_get_block, wbc);
-
-	if (!ret && inode->i_size > EXT4_I(inode)->i_disksize) {
-		EXT4_I(inode)->i_disksize = inode->i_size;
-		ext4_mark_inode_dirty(handle, inode);
-	}
+		ret = block_write_full_page(page, ext4_da_get_block_write, wbc);
 
-	err = ext4_journal_stop(handle);
-	if (!ret)
-		ret = err;
-	return ret;
-
-out_fail:
-	redirty_page_for_writepage(wbc, page);
-	unlock_page(page);
 	return ret;
 }
 
+
+/*
+ * For now just follow the DIO way to estimate the max credits
+ * needed to write out EXT4_MAX_WRITEBACK_PAGES.
+ * todo: need to calculate the max credits need for
+ * extent based files, currently the DIO credits is based on
+ * indirect-blocks mapping way.
+ *
+ * Probably should have a generic way to calculate credits
+ * for DIO, writepages, and truncate
+ */
+#define EXT4_MAX_WRITEBACK_PAGES      DIO_MAX_BLOCKS
+#define EXT4_MAX_WRITEBACK_CREDITS    DIO_CREDITS
+
 static int ext4_da_writepages(struct address_space *mapping,
 				struct writeback_control *wbc)
 {
-	return mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+	struct inode *inode = mapping->host;
+	handle_t *handle = NULL;
+	int needed_blocks;
+	int ret = 0;
+	long to_write;
+	loff_t range_start = 0;
+
+	/*
+	 * No pages to write? This is mainly a kludge to avoid starting
+	 * a transaction for special inodes like journal inode on last iput()
+	 * because that could violate lock ordering on umount
+	 */
+	if (!mapping->nrpages)
+		return 0;
+
+	/*
+	 *  Estimate the worse case needed credits to write out
+	 * EXT4_MAX_BUF_BLOCKS pages
+	 */
+	needed_blocks = EXT4_MAX_WRITEBACK_CREDITS;
+
+	to_write = wbc->nr_to_write;
+	if (!wbc->range_cyclic) {
+		/*
+		 * If range_cyclic is not set force range_cont
+		 * and save the old writeback_index
+		 */
+		wbc->range_cont = 1;
+		range_start =  wbc->range_start;
+	}
+
+	while (!ret && to_write) {
+		/* start a new transaction*/
+		handle = ext4_journal_start(inode, needed_blocks);
+		if (IS_ERR(handle)) {
+			ret = PTR_ERR(handle);
+			goto out_writepages;
+		}
+		/*
+		 * set the max dirty pages could be write at a time
+		 * to fit into the reserved transaction credits
+		 */
+		if (wbc->nr_to_write > EXT4_MAX_WRITEBACK_PAGES)
+			wbc->nr_to_write = EXT4_MAX_WRITEBACK_PAGES;
+
+		to_write -= wbc->nr_to_write;
+		ret = mpage_da_writepages(mapping, wbc,
+						ext4_da_get_block_write);
+		ext4_journal_stop(handle);
+		if (wbc->nr_to_write) {
+			/*
+			 * There is no more writeout needed
+			 * or we requested for a noblocking writeout
+			 * and we found the device congested
+			 */
+			to_write += wbc->nr_to_write;
+			break;
+		}
+		wbc->nr_to_write = to_write;
+	}
+
+out_writepages:
+	wbc->nr_to_write = to_write;
+	if (range_start)
+		wbc->range_start = range_start;
+	return ret;
 }
 
 static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
@@ -2137,11 +2229,6 @@ out:
 	return ret;
 }
 
-static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
-{
-	return !buffer_mapped(bh) || buffer_delay(bh);
-}
-
 static int ext4_da_write_end(struct file *file,
 				struct address_space *mapping,
 				loff_t pos, unsigned len, unsigned copied,