ext4: fix ZERO_RANGE bug hidden by flag aliasing

We accidently aliased EXT4_EX_NOCACHE and EXT4_GET_CONVERT_UNWRITTEN
falgs, which apparently was hiding a bug that was unmasked when this
flag aliasing issue was addressed (see the subsequent commit).  The
reproduction case was:

   fsx -N 10000 -l 500000 -r 4096 -t 4096 -w 4096 -Z -R -W /vdb/junk

... which would cause fsx to report corruption in the data file.

The fix we have is a bit of an overkill, but I'd much rather be
conservative for now, and we can optimize ZERO_RANGE_FL handling
later.  The fact that we need to zap the extent_status cache for the
inode is unfortunate, but correctness is far more important than
performance.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: Namjae Jeon <namjae.jeon@samsung.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index d00937336f19..bf205f72be35 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4802,7 +4802,8 @@ static long ext4_zero_range(struct file *file, loff_t offset,
                 max_blocks -= lblk;
 
         flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
-                EXT4_GET_BLOCKS_CONVERT_UNWRITTEN;
+                EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
+                EXT4_EX_NOCACHE;
         if (mode & FALLOC_FL_KEEP_SIZE)
                 flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
 
@@ -4840,15 +4841,21 @@ static long ext4_zero_range(struct file *file, loff_t offset,
                 ext4_inode_block_unlocked_dio(inode);
                 inode_dio_wait(inode);
 
+                ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
+                                             flags, mode);
+                if (ret)
+                        goto out_dio;
                 /*
                  * Remove entire range from the extent status tree.
+                 *
+                 * ext4_es_remove_extent(inode, lblk, max_blocks) is
+                 * NOT sufficient.  I'm not sure why this is the case,
+                 * but let's be conservative and remove the extent
+                 * status tree for the entire inode.  There should be
+                 * no outstanding delalloc extents thanks to the
+                 * filemap_write_and_wait_range() call above.
                  */
-                ret = ext4_es_remove_extent(inode, lblk, max_blocks);
-                if (ret)
-                        goto out_dio;
-
-                ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
-                                             flags, mode);
+                ret = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
                 if (ret)
                         goto out_dio;
         }