FAILED: patch "[PATCH] ext4: convert to exclusive lock while inserting delalloc" failed to apply to 6.6-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x acf795dc161f3cf481db20f05db4250714e375e5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024021923-unlined-visibly-5e4c@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

acf795dc161f ("ext4: convert to exclusive lock while inserting delalloc extents")
3fcc2b887a1b ("ext4: refactor ext4_da_map_blocks()")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From acf795dc161f3cf481db20f05db4250714e375e5 Mon Sep 17 00:00:00 2001
From: Zhang Yi <yi.zhang@xxxxxxxxxx>
Date: Sat, 27 Jan 2024 09:58:01 +0800
Subject: [PATCH] ext4: convert to exclusive lock while inserting delalloc
 extents

ext4_da_map_blocks() only hold i_data_sem in shared mode and i_rwsem
when inserting delalloc extents, it could be raced by another querying
path of ext4_map_blocks() without i_rwsem, .e.g buffered read path.
Suppose we buffered read a file containing just a hole, and without any
cached extents tree, then it is raced by another delayed buffered write
to the same area or the near area belongs to the same hole, and the new
delalloc extent could be overwritten to a hole extent.

 pread()                           pwrite()
  filemap_read_folio()
   ext4_mpage_readpages()
    ext4_map_blocks()
     down_read(i_data_sem)
     ext4_ext_determine_hole()
     //find hole
     ext4_ext_put_gap_in_cache()
      ext4_es_find_extent_range()
      //no delalloc extent
                                    ext4_da_map_blocks()
                                     down_read(i_data_sem)
                                     ext4_insert_delayed_block()
                                     //insert delalloc extent
      ext4_es_insert_extent()
      //overwrite delalloc extent to hole

This race could lead to inconsistent delalloc extents tree and
incorrect reserved space counter. Fix this by converting to hold
i_data_sem in exclusive mode when adding a new delalloc extent in
ext4_da_map_blocks().

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Suggested-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/20240127015825.1608160-3-yi.zhang@xxxxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bbd5ee6dd3f3..b040337501e3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1703,10 +1703,8 @@ static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
 
 	/* Lookup extent status tree firstly */
 	if (ext4_es_lookup_extent(inode, iblock, NULL, &es)) {
-		if (ext4_es_is_hole(&es)) {
-			down_read(&EXT4_I(inode)->i_data_sem);
+		if (ext4_es_is_hole(&es))
 			goto add_delayed;
-		}
 
 		/*
 		 * Delayed extent could be allocated by fallocate.
@@ -1748,8 +1746,10 @@ static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
 		retval = ext4_ext_map_blocks(NULL, inode, map, 0);
 	else
 		retval = ext4_ind_map_blocks(NULL, inode, map, 0);
-	if (retval < 0)
-		goto out_unlock;
+	if (retval < 0) {
+		up_read(&EXT4_I(inode)->i_data_sem);
+		return retval;
+	}
 	if (retval > 0) {
 		unsigned int status;
 
@@ -1765,24 +1765,21 @@ static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
 				EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
 		ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
 				      map->m_pblk, status);
-		goto out_unlock;
+		up_read(&EXT4_I(inode)->i_data_sem);
+		return retval;
 	}
+	up_read(&EXT4_I(inode)->i_data_sem);
 
 add_delayed:
-	/*
-	 * XXX: __block_prepare_write() unmaps passed block,
-	 * is it OK?
-	 */
+	down_write(&EXT4_I(inode)->i_data_sem);
 	retval = ext4_insert_delayed_block(inode, map->m_lblk);
+	up_write(&EXT4_I(inode)->i_data_sem);
 	if (retval)
-		goto out_unlock;
+		return retval;
 
 	map_bh(bh, inode->i_sb, invalid_block);
 	set_buffer_new(bh);
 	set_buffer_delay(bh);
-
-out_unlock:
-	up_read((&EXT4_I(inode)->i_data_sem));
 	return retval;
 }