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: 845abeb1f06a ("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>

diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
index 8c541ca718722d64a44c156db71da751209121d0..81c94dd1d5966bc97ee320f42905fa6ad99c483d 100644 (file)
--- a/fs/xfs/xfs_zone_gc.c
+++ b/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;