ext4: Provide function to handle transaction restarts

Provide ext4_journal_ensure_credits_fn() function to ensure transaction
has given amount of credits and call helper function to prepare for
restarting a transaction. This allows to remove some boilerplate code
from various places, add proper error handling for the case where
transaction extension or restart fails, and reduces following changes
needed for proper revoke record reservation tracking.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20191105164437.32602-10-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 54 insertions, 39 deletions

diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 602abae08387..63e1d5846442 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -699,27 +699,62 @@ int ext4_ind_trans_blocks(struct inode *inode, int nrblocks)
 	return DIV_ROUND_UP(nrblocks, EXT4_ADDR_PER_BLOCK(inode->i_sb)) + 4;
 }
 
+static int ext4_ind_trunc_restart_fn(handle_t *handle, struct inode *inode,
+				     struct buffer_head *bh, int *dropped)
+{
+	int err;
+
+	if (bh) {
+		BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
+		err = ext4_handle_dirty_metadata(handle, inode, bh);
+		if (unlikely(err))
+			return err;
+	}
+	err = ext4_mark_inode_dirty(handle, inode);
+	if (unlikely(err))
+		return err;
+	/*
+	 * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
+	 * moment, get_block can be called only for blocks inside i_size since
+	 * page cache has been already dropped and writes are blocked by
+	 * i_mutex. So we can safely drop the i_data_sem here.
+	 */
+	BUG_ON(EXT4_JOURNAL(inode) == NULL);
+	ext4_discard_preallocations(inode);
+	up_write(&EXT4_I(inode)->i_data_sem);
+	*dropped = 1;
+	return 0;
+}
+
 /*
  * Truncate transactions can be complex and absolutely huge.  So we need to
  * be able to restart the transaction at a conventient checkpoint to make
  * sure we don't overflow the journal.
  *
  * Try to extend this transaction for the purposes of truncation.  If
- * extend fails, we need to propagate the failure up and restart the
- * transaction in the top-level truncate loop. --sct
- *
- * Returns 0 if we managed to create more room.  If we can't create more
- * room, and the transaction must be restarted we return 1.
+ * extend fails, we restart transaction.
  */
-static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
+static int ext4_ind_truncate_ensure_credits(handle_t *handle,
+					    struct inode *inode,
+					    struct buffer_head *bh)
 {
-	if (!ext4_handle_valid(handle))
-		return 0;
-	if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
-		return 0;
-	if (!ext4_journal_extend(handle, ext4_blocks_for_truncate(inode)))
-		return 0;
-	return 1;
+	int ret;
+	int dropped = 0;
+
+	ret = ext4_journal_ensure_credits_fn(handle, EXT4_RESERVE_TRANS_BLOCKS,
+			ext4_blocks_for_truncate(inode),
+			ext4_ind_trunc_restart_fn(handle, inode, bh, &dropped));
+	if (dropped)
+		down_write(&EXT4_I(inode)->i_data_sem);
+	if (ret <= 0)
+		return ret;
+	if (bh) {
+		BUFFER_TRACE(bh, "retaking write access");
+		ret = ext4_journal_get_write_access(handle, bh);
+		if (unlikely(ret))
+			return ret;
+	}
+	return 0;
 }
 
 /*
@@ -854,27 +889,9 @@ static int ext4_clear_blocks(handle_t *handle, struct inode *inode,
 		return 1;
 	}
 
-	if (try_to_extend_transaction(handle, inode)) {
-		if (bh) {
-			BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
-			err = ext4_handle_dirty_metadata(handle, inode, bh);
-			if (unlikely(err))
-				goto out_err;
-		}
-		err = ext4_mark_inode_dirty(handle, inode);
-		if (unlikely(err))
-			goto out_err;
-		err = ext4_truncate_restart_trans(handle, inode,
-					ext4_blocks_for_truncate(inode));
-		if (unlikely(err))
-			goto out_err;
-		if (bh) {
-			BUFFER_TRACE(bh, "retaking write access");
-			err = ext4_journal_get_write_access(handle, bh);
-			if (unlikely(err))
-				goto out_err;
-		}
-	}
+	err = ext4_ind_truncate_ensure_credits(handle, inode, bh);
+	if (err < 0)
+		goto out_err;
 
 	for (p = first; p < last; p++)
 		*p = 0;
@@ -1057,11 +1074,9 @@ static void ext4_free_branches(handle_t *handle, struct inode *inode,
 			 */
 			if (ext4_handle_is_aborted(handle))
 				return;
-			if (try_to_extend_transaction(handle, inode)) {
-				ext4_mark_inode_dirty(handle, inode);
-				ext4_truncate_restart_trans(handle, inode,
-					    ext4_blocks_for_truncate(inode));
-			}
+			if (ext4_ind_truncate_ensure_credits(handle, inode,
+							     NULL) < 0)
+				return;
 
 			/*
 			 * The forget flag here is critical because if