On 28 Jan 2021 at 23:14, Darrick J. Wong wrote:

On Thu, Jan 28, 2021 at 10:34:12AM -0500, Brian Foster wrote:

quoted

On Wed, Jan 27, 2021 at 02:35:37PM +0530, Chandan Babu R wrote:

quoted

With both CONFIG_XFS_DEBUG and CONFIG_XFS_WARN disabled, the only reference to
local variable "error" in xfs_bmap_compute_alignments() gets eliminated during
pre-processing stage of the compilation process. This causes the compiler to
generate a "set but not used" warning.

Reported-by: kernel test robot <redacted>
Signed-off-by: Chandan Babu R <redacted>
---
This patch is applicable on top of current xfs-linux/for-next branch.

 fs/xfs/libxfs/xfs_bmap.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 2cd24bb06040..ba56554e8c05 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c

@@ -3471,7 +3471,6 @@ xfs_bmap_compute_alignments(
 	struct xfs_mount	*mp = args->mp;
 	xfs_extlen_t		align = 0; /* minimum allocation alignment */
 	int			stripe_align = 0;
-	int			error;

 	/* stripe alignment for allocation is determined by mount parameters */
 	if (mp->m_swidth && (mp->m_flags & XFS_MOUNT_SWALLOC))

@@ -3484,10 +3483,10 @@ xfs_bmap_compute_alignments(
 	else if (ap->datatype & XFS_ALLOC_USERDATA)
 		align = xfs_get_extsz_hint(ap->ip);
 	if (align) {
-		error = xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
-						align, 0, ap->eof, 0, ap->conv,
-						&ap->offset, &ap->length);
-		ASSERT(!error);
+		if (xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
+			align, 0, ap->eof, 0, ap->conv, &ap->offset,
+			&ap->length))
+			ASSERT(0);

I was wondering if we should just make xfs_bmap_extsize_align() return
void and push the asserts down into the function itself, but it looks
like xfs_bmap_rtalloc() actually handles the error. Any idea on why we
might have that inconsistency?

It only returns nonzero if isrt (the fifth parameter) is nonzero, and
only if the requested range is still not aligned to the rt extent size
after aligning it and eliminating any overlaps with existing extents.

Adding to what Darrick has mentioned above ...

Space on realtime devices are tracked at a granularity of "rextsize"
bytes. Each bit held in the data blocks of xfs_mount->m_rbmip represents usage
status of a single rextsized block. Most likely this seems to be underlying
reason for strict allocation alignment requirements for realtime files.

--
chandan