ext4: get rid of EXT4_GET_BLOCKS_NO_LOCK flag

When dioread_nolock mode is enabled, we grab i_data_sem in
ext4_ext_direct_IO() and therefore we need to instruct _ext4_get_block()
not to grab i_data_sem again using EXT4_GET_BLOCKS_NO_LOCK. However
holding i_data_sem over overwrite direct IO isn't needed these days. We
have exclusion against truncate / hole punching because we increase
i_dio_count under i_mutex in ext4_ext_direct_IO() so once
ext4_file_write_iter() verifies blocks are allocated & written, they are
guaranteed to stay so during the whole direct IO even after we drop
i_mutex.

So we can just remove this locking abuse and the no longer necessary
EXT4_GET_BLOCKS_NO_LOCK flag.
Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -555,10 +555,8 @@ enum {
 #define EXT4_GET_BLOCKS_NO_NORMALIZE		0x0040
 	/* Request will not result in inode size update (user for fallocate) */
 #define EXT4_GET_BLOCKS_KEEP_SIZE		0x0080
-	/* Do not take i_data_sem locking in ext4_map_blocks */
-#define EXT4_GET_BLOCKS_NO_LOCK			0x0100
 	/* Convert written extents to unwritten */
-#define EXT4_GET_BLOCKS_CONVERT_UNWRITTEN	0x0200
+#define EXT4_GET_BLOCKS_CONVERT_UNWRITTEN	0x0100
 
 /*
  * The bit position of these flags must not overlap with any of the

fs/ext4/inode.c

@@ -403,7 +403,6 @@ static void ext4_map_blocks_es_recheck(handle_t *handle,
 	 * out taking i_data_sem.  So at the time the unwritten extent
 	 * could be converted.
 	 */
-	if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
 	down_read(&EXT4_I(inode)->i_data_sem);
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 		retval = ext4_ext_map_blocks(handle, inode, map, flags &
@@ -412,7 +411,6 @@ static void ext4_map_blocks_es_recheck(handle_t *handle,
 		retval = ext4_ind_map_blocks(handle, inode, map, flags &
 					     EXT4_GET_BLOCKS_KEEP_SIZE);
 	}
-	if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
 	up_read((&EXT4_I(inode)->i_data_sem));
 
 	/*
@@ -509,7 +507,6 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
 	 * Try to see if we can get the block without requesting a new
 	 * file system block.
 	 */
-	if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
 	down_read(&EXT4_I(inode)->i_data_sem);
 	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 		retval = ext4_ext_map_blocks(handle, inode, map, flags &
@@ -541,7 +538,6 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
 		if (ret < 0)
 			retval = ret;
 	}
-	if (!(flags & EXT4_GET_BLOCKS_NO_LOCK))
 	up_read((&EXT4_I(inode)->i_data_sem));
 
 found:
@@ -674,7 +670,7 @@ static int _ext4_get_block(struct inode *inode, sector_t iblock,
 	map.m_lblk = iblock;
 	map.m_len = bh->b_size >> inode->i_blkbits;
 
-	if (flags && !(flags & EXT4_GET_BLOCKS_NO_LOCK) && !handle) {
+	if (flags && !handle) {
 		/* Direct IO write... */
 		if (map.m_len > DIO_MAX_BLOCKS)
 			map.m_len = DIO_MAX_BLOCKS;
@@ -879,9 +875,6 @@ int do_journal_get_write_access(handle_t *handle,
 	return ret;
 }
 
-static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
-		   struct buffer_head *bh_result, int create);
-
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len,
 				  get_block_t *get_block)
@@ -3054,13 +3047,21 @@ int ext4_get_block_write(struct inode *inode, sector_t iblock,
 			       EXT4_GET_BLOCKS_IO_CREATE_EXT);
 }
 
-static int ext4_get_block_write_nolock(struct inode *inode, sector_t iblock,
+static int ext4_get_block_overwrite(struct inode *inode, sector_t iblock,
 		   struct buffer_head *bh_result, int create)
 {
-	ext4_debug("ext4_get_block_write_nolock: inode %lu, create flag %d\n",
+	int ret;
+
+	ext4_debug("ext4_get_block_overwrite: inode %lu, create flag %d\n",
 		   inode->i_ino, create);
-	return _ext4_get_block(inode, iblock, bh_result,
-			       EXT4_GET_BLOCKS_NO_LOCK);
+	ret = _ext4_get_block(inode, iblock, bh_result, 0);
+	/*
+	 * Blocks should have been preallocated! ext4_file_write_iter() checks
+	 * that.
+	 */
+	WARN_ON_ONCE(!buffer_mapped(bh_result));
+
+	return ret;
 }
 
 int ext4_get_block_dax(struct inode *inode, sector_t iblock,
@@ -3143,10 +3144,8 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	/* If we do a overwrite dio, i_mutex locking can be released */
 	overwrite = *((int *)iocb->private);
 
-	if (overwrite) {
-		down_read(&EXT4_I(inode)->i_data_sem);
+	if (overwrite)
 		mutex_unlock(&inode->i_mutex);
-	}
 
 	/*
 	 * We could direct write to holes and fallocate.
@@ -3189,7 +3188,7 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	}
 
 	if (overwrite) {
-		get_block_func = ext4_get_block_write_nolock;
+		get_block_func = ext4_get_block_overwrite;
 	} else {
 		get_block_func = ext4_get_block_write;
 		dio_flags = DIO_LOCKING;
@@ -3245,10 +3244,8 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	if (iov_iter_rw(iter) == WRITE)
 		inode_dio_end(inode);
 	/* take i_mutex locking again if we do a ovewrite dio */
-	if (overwrite) {
-		up_read(&EXT4_I(inode)->i_data_sem);
+	if (overwrite)
 		mutex_lock(&inode->i_mutex);
-	}
 
 	return ret;
 }

include/trace/events/ext4.h

@@ -42,8 +42,7 @@ struct extent_status;
 	{ EXT4_GET_BLOCKS_CONVERT,		"CONVERT" },		\
 	{ EXT4_GET_BLOCKS_METADATA_NOFAIL,	"METADATA_NOFAIL" },	\
 	{ EXT4_GET_BLOCKS_NO_NORMALIZE,		"NO_NORMALIZE" },	\
-	{ EXT4_GET_BLOCKS_KEEP_SIZE,		"KEEP_SIZE" },		\
-	{ EXT4_GET_BLOCKS_NO_LOCK,		"NO_LOCK" })
+	{ EXT4_GET_BLOCKS_KEEP_SIZE,		"KEEP_SIZE" })
 
 #define show_mflags(flags) __print_flags(flags, "",	\
 	{ EXT4_MAP_NEW,		"N" },			\