XFS: fix zoned gc threshold math for 32-bit arches

xfs_zoned_need_gc makes use of mult_frac() to calculate the threshold
for triggering the zoned garbage collector, but, turns out mult_frac()
doesn't properly work with 64-bit data types and this caused build
failures on some 32-bit architectures.

Fix this by essentially open coding mult_frac() in a 64-bit friendly
way.

Notice we don't need to bother with counters underflow here because
xfs_estimate_freecounter() will always return a positive value, as it
leverages percpu_counter_read_positive to read such counters.

Fixes: 845abeb ("xfs: add tunable threshold parameter for triggering zone GC")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504181233.F7D9Atra-lkp@intel.com/
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: cmaiolino

fs/xfs/xfs_zone_gc.c

@@ -170,7 +170,8 @@ bool
 xfs_zoned_need_gc(
 	struct xfs_mount	*mp)
 {
-	s64			available, free;
+	s64			available, free, threshold;
+	s32			remainder;
 
 	if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_RECLAIMABLE))
 		return false;
@@ -183,7 +184,12 @@ xfs_zoned_need_gc(
 		return true;
 
 	free = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS);
-	if (available < mult_frac(free, mp->m_zonegc_low_space, 100))
+
+	threshold = div_s64_rem(free, 100, &remainder);
+	threshold = threshold * mp->m_zonegc_low_space +
+		    remainder * div_s64(mp->m_zonegc_low_space, 100);
+
+	if (available < threshold)
 		return true;
 
 	return false;