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>

2 files changed, 21 insertions, 26 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 80f76f092079..1008caf3136d 100644
--- a/fs/ext4/ext4.h
+++ b/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
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 472e608da13d..f100c1780e03 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -403,8 +403,7 @@ 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);
+        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 &
                                              EXT4_GET_BLOCKS_KEEP_SIZE);
@@ -412,8 +411,7 @@ 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));
+        up_read((&EXT4_I(inode)->i_data_sem));
 
         /*
          * We don't check m_len because extent will be collpased in status
@@ -509,8 +507,7 @@ 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);
+        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 &
                                              EXT4_GET_BLOCKS_KEEP_SIZE);
@@ -541,8 +538,7 @@ 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));
+        up_read((&EXT4_I(inode)->i_data_sem));
 
 found:
         if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
@@ -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 @@ retake_lock:
         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;
 }