xfs: error tag to force zeroing on debug kernels

iomap_zero_range() has to cover various corner cases that are
difficult to test on production kernels because it is used in fairly
limited use cases. For example, it is currently only used by XFS and
mostly only in partial block zeroing cases.

While it's possible to test most of these functional cases, we can
provide more robust test coverage by co-opting fallocate zero range
to invoke zeroing of the entire range instead of the more efficient
block punch/allocate sequence. Add an errortag to occasionally
invoke forced zeroing.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 26 insertions, 9 deletions

diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
index de840abc0bcd..57e47077c75a 100644
--- a/fs/xfs/libxfs/xfs_errortag.h
+++ b/fs/xfs/libxfs/xfs_errortag.h
@@ -73,7 +73,8 @@
 #define XFS_ERRTAG_WRITE_DELAY_MS			43
 #define XFS_ERRTAG_EXCHMAPS_FINISH_ONE			44
 #define XFS_ERRTAG_METAFILE_RESV_CRITICAL		45
-#define XFS_ERRTAG_MAX					46
+#define XFS_ERRTAG_FORCE_ZERO_RANGE			46
+#define XFS_ERRTAG_MAX					47
 
 /*
  * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
@@ -133,7 +134,8 @@ XFS_ERRTAG(ATTR_LEAF_TO_NODE,	attr_leaf_to_node,	1) \
 XFS_ERRTAG(WB_DELAY_MS,		wb_delay_ms,		3000) \
 XFS_ERRTAG(WRITE_DELAY_MS,	write_delay_ms,		3000) \
 XFS_ERRTAG(EXCHMAPS_FINISH_ONE,	exchmaps_finish_one,	1) \
-XFS_ERRTAG(METAFILE_RESV_CRITICAL, metafile_resv_crit,	4)
+XFS_ERRTAG(METAFILE_RESV_CRITICAL, metafile_resv_crit,	4) \
+XFS_ERRTAG(FORCE_ZERO_RANGE,	force_zero_range,	4)
 #endif /* XFS_ERRTAG */
 
 #endif /* __XFS_ERRORTAG_H_ */
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 2702fef2c90c..5b9864c8582e 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -27,6 +27,8 @@
 #include "xfs_file.h"
 #include "xfs_aops.h"
 #include "xfs_zone_alloc.h"
+#include "xfs_error.h"
+#include "xfs_errortag.h"
 
 #include <linux/dax.h>
 #include <linux/falloc.h>
@@ -1254,23 +1256,36 @@ xfs_falloc_zero_range(
 	struct xfs_zone_alloc_ctx *ac)
 {
 	struct inode		*inode = file_inode(file);
+	struct xfs_inode	*ip = XFS_I(inode);
 	unsigned int		blksize = i_blocksize(inode);
 	loff_t			new_size = 0;
 	int			error;
 
-	trace_xfs_zero_file_space(XFS_I(inode));
+	trace_xfs_zero_file_space(ip);
 
 	error = xfs_falloc_newsize(file, mode, offset, len, &new_size);
 	if (error)
 		return error;
 
-	error = xfs_free_file_space(XFS_I(inode), offset, len, ac);
-	if (error)
-		return error;
+	/*
+	 * Zero range implements a full zeroing mechanism but is only used in
+	 * limited situations. It is more efficient to allocate unwritten
+	 * extents than to perform zeroing here, so use an errortag to randomly
+	 * force zeroing on DEBUG kernels for added test coverage.
+	 */
+	if (XFS_TEST_ERROR(ip->i_mount,
+			   XFS_ERRTAG_FORCE_ZERO_RANGE)) {
+		error = xfs_zero_range(ip, offset, len, ac, NULL);
+	} else {
+		error = xfs_free_file_space(ip, offset, len, ac);
+		if (error)
+			return error;
 
-	len = round_up(offset + len, blksize) - round_down(offset, blksize);
-	offset = round_down(offset, blksize);
-	error = xfs_alloc_file_space(XFS_I(inode), offset, len);
+		len = round_up(offset + len, blksize) -
+			round_down(offset, blksize);
+		offset = round_down(offset, blksize);
+		error = xfs_alloc_file_space(ip, offset, len);
+	}
 	if (error)
 		return error;
 	return xfs_falloc_setsize(file, new_size);