Re: [PATCH] ext4: stop return ENOSPC from ext4_issue_zeroout

On Wed, Aug 04, 2021 at 03:35:29PM +0200, Jan Kara wrote:

On Wed 04-08-21 20:50:44, yangerkun wrote:

quoted

Our testcase(briefly described as fsstress on dm thin-provisioning which
ext4 see volume size with 100G but actual size 10G) trigger a hungtask
bug since ext4_writepages fall into a infinite loop:

Got ENOSPC with follow stack:
...
ext4_ext_map_blocks
  ext4_ext_convert_to_initialized
    ext4_ext_zeroout
      ext4_issue_zeroout
        ...
        submit_bio_wait <-- bio to thinpool will return ENOSPC

Thanks for the patch. As a quick fix for the problem this is probably fine.
But longer term we might need to implement a configurable behavior for this
because just dropping data on the floor (which is what would happen here)
need not be what sysadmin wants and blocking until space is provisioned may be
actually a preferable behavior. Anyway for now feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Hmm, I wonder if this would be a better fix.  (Not yet tested, may fry
your file system, etc....)   What do folks think?

						- Ted

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 92ad64b89d9b..501516cadc1b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c

@@ -3569,7 +3569,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 				split_map.m_len - ee_block);
 			err = ext4_ext_zeroout(inode, &zero_ex1);
 			if (err)
-				goto out;
+				goto fallback;
 			split_map.m_len = allocated;
 		}
 		if (split_map.m_lblk - ee_block + split_map.m_len <

@@ -3583,7 +3583,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 						      ext4_ext_pblock(ex));
 				err = ext4_ext_zeroout(inode, &zero_ex2);
 				if (err)
-					goto out;
+					goto fallback;
 			}
 
 			split_map.m_len += split_map.m_lblk - ee_block;

@@ -3592,6 +3592,7 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 		}
 	}
 
+fallback:
 	err = ext4_split_extent(handle, inode, ppath, &split_map, split_flag,
 				flags);
 	if (err > 0)