[f2fs-dev] [PATCH] f2fs: fix to tag STATX_DIOALIGN only if inode support dio

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

After commit 5c8764f8679e ("f2fs: fix to force buffered IO on inline_data
inode"), f2fs starts to force using buffered IO on inline_data inode.

And also, it will cause f2fs_getattr() returning invalid zeroed value on
.dio_mem_align and .dio_offset_align fields, however, STATX_DIOALIGN flag
was been tagged. User may use zeroed .stx_dio_offset_align value
since STATX_DIOALIGN was been tagged, then it causes a deadloop during
generic/465 test due to below logic:

align=stx_dio_offset_align(it equals to zero)
page_size=4096
while [ $align -le $page_size ]; do
	echo "$AIO_TEST -a $align -d $testfile.$align" >> $seqres.full
	$AIO_TEST -a $align -d $testfile.$align 2>&1 | tee -a $seqres.full
	align=$((align * 2))
done

Quoted from description of statx manual:

" If  a  filesystem  does  not support a field or if it has an
  unrepresentable value (for instance, a file with an exotic type),
  then the mask bit corresponding to that field will be cleared in
  stx_mask even if the user asked for it and a dummy value will be
  filled in for compatibility purposes if one is available (e.g.,
  a dummy UID and GID may be specified to mount under some
  circumstances)."

We should not set STATX_DIOALIGN flag in kstat.stx_mask if inode
does not support DIO, so that it can indicate related fields contain
dummy value, and avoid following incorrect use of them.

Fixes: c8c02272a9f7 ("f2fs: support STATX_DIOALIGN")
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/file.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 99903eafa7fe..f0b8b77e93ba 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -906,14 +906,11 @@ int f2fs_getattr(struct mnt_idmap *idmap, const struct path *path,
 	 * f2fs sometimes supports DIO reads but not DIO writes.  STATX_DIOALIGN
 	 * cannot represent that, so in that case we report no DIO support.
 	 */
-	if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode)) {
-		unsigned int bsize = i_blocksize(inode);
-
+	if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode) &&
+				!f2fs_force_buffered_io(inode, WRITE)) {
+		stat->dio_mem_align = F2FS_BLKSIZE;
+		stat->dio_offset_align = F2FS_BLKSIZE;
 		stat->result_mask |= STATX_DIOALIGN;
-		if (!f2fs_force_buffered_io(inode, WRITE)) {
-			stat->dio_mem_align = bsize;
-			stat->dio_offset_align = bsize;
-		}
 	}
 
 	flags = fi->i_flags;
-- 
2.40.1



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