ext4: use pre-zeroed blocks for DAX page faults
Make DAX fault path use pre-zeroed blocks to avoid races with extent
conversion and zeroing when two page faults to the same block happen.
Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4241d0c..ff2f3cd 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -723,16 +723,6 @@
map_bh(bh, inode->i_sb, map.m_pblk);
bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
- if (IS_DAX(inode) && buffer_unwritten(bh)) {
- /*
- * dgc: I suspect unwritten conversion on ext4+DAX is
- * fundamentally broken here when there are concurrent
- * read/write in progress on this inode.
- */
- WARN_ON_ONCE(io_end);
- bh->b_assoc_map = inode->i_mapping;
- bh->b_private = (void *)(unsigned long)iblock;
- }
if (io_end && io_end->flag & EXT4_IO_END_UNWRITTEN)
set_buffer_defer_completion(bh);
bh->b_size = inode->i_sb->s_blocksize * map.m_len;
@@ -3097,17 +3087,79 @@
return ret;
}
-int ext4_get_block_dax(struct inode *inode, sector_t iblock,
- struct buffer_head *bh_result, int create)
+#ifdef CONFIG_FS_DAX
+int ext4_dax_mmap_get_block(struct inode *inode, sector_t iblock,
+ struct buffer_head *bh_result, int create)
{
- int flags = EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_UNWRIT_EXT;
+ int ret, err;
+ int credits;
+ struct ext4_map_blocks map;
+ handle_t *handle = NULL;
+ int flags = 0;
- if (create)
- flags |= EXT4_GET_BLOCKS_CREATE;
- ext4_debug("ext4_get_block_dax: inode %lu, create flag %d\n",
+ ext4_debug("ext4_dax_mmap_get_block: inode %lu, create flag %d\n",
inode->i_ino, create);
- return _ext4_get_block(inode, iblock, bh_result, flags);
+ map.m_lblk = iblock;
+ map.m_len = bh_result->b_size >> inode->i_blkbits;
+ credits = ext4_chunk_trans_blocks(inode, map.m_len);
+ if (create) {
+ flags |= EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_CREATE_ZERO;
+ handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ return ret;
+ }
+ }
+
+ ret = ext4_map_blocks(handle, inode, &map, flags);
+ if (create) {
+ err = ext4_journal_stop(handle);
+ if (ret >= 0 && err < 0)
+ ret = err;
+ }
+ if (ret <= 0)
+ goto out;
+ if (map.m_flags & EXT4_MAP_UNWRITTEN) {
+ int err2;
+
+ /*
+ * We are protected by i_mmap_sem so we know block cannot go
+ * away from under us even though we dropped i_data_sem.
+ * Convert extent to written and write zeros there.
+ *
+ * Note: We may get here even when create == 0.
+ */
+ handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ goto out;
+ }
+
+ err = ext4_map_blocks(handle, inode, &map,
+ EXT4_GET_BLOCKS_CONVERT | EXT4_GET_BLOCKS_CREATE_ZERO);
+ if (err < 0)
+ ret = err;
+ err2 = ext4_journal_stop(handle);
+ if (err2 < 0 && ret > 0)
+ ret = err2;
+ }
+out:
+ WARN_ON_ONCE(ret == 0 && create);
+ if (ret > 0) {
+ map_bh(bh_result, inode->i_sb, map.m_pblk);
+ bh_result->b_state = (bh_result->b_state & ~EXT4_MAP_FLAGS) |
+ map.m_flags;
+ /*
+ * At least for now we have to clear BH_New so that DAX code
+ * doesn't attempt to zero blocks again in a racy way.
+ */
+ bh_result->b_state &= ~(1 << BH_New);
+ bh_result->b_size = map.m_len << inode->i_blkbits;
+ ret = 0;
+ }
+ return ret;
}
+#endif
static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
ssize_t size, void *private)