[PATCH v6 1/2] badblocks: fix in-place round_up/round_down usage bug

[Ramesh Adhikari <adhikari.resume@gmail.com>]

rounddown() and roundup() do not modify their first argument in
place; they return the rounded value. _badblocks_set(),
_badblocks_clear() and badblocks_check() were calling them as
bare statements and discarding the result, so 's' (and 'next'/
'target') were never actually rounded. Depending on the caller's
alignment this can leave 'sectors' unchanged or, in the reported
case, produce a range whose end never advances, causing
_badblocks_check()/badblocks_check() to loop with a non-advancing
cursor and stall the CPU (RCU stall) when called through the
nvdimm ioctl path via nvdimm_clear_badblocks_region().

rounddown()/roundup() also do division/modulo on the sector_t
(u64) operand, which requires libgcc helpers (__aeabi_uldivmod,
__umoddi3) that are not linked into the kernel on 32-bit builds,
breaking the build on arm/i386 (reported by kernel test robot).

Switch to round_down()/round_up() (include/linux/math.h), which
are mask-based, assign their result back to the variable being
rounded, and require no 64-bit division, fixing both the
non-rounding bug and the 32-bit build breakage.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202604301231.IpPh4AiH-lkp@intel.com/
Fixes: aa511ff8218b ("badblocks: switch to the improved badblock handling code")
Cc: stable@vger.kernel.org
Signed-off-by: Ramesh Adhikari <adhikari.resume@gmail.com>
---
 block/badblocks.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/badblocks.c b/block/badblocks.c
index ece64e76fe8..1f786b193fb 100644
--- a/block/badblocks.c
+++ b/block/badblocks.c
@@ -857,8 +857,8 @@ static bool _badblocks_set(struct badblocks *bb, sector_t s, sector_t sectors,
 		/* round the start down, and the end up */
 		sector_t next = s + sectors;
 
-		rounddown(s, 1 << bb->shift);
-		roundup(next, 1 << bb->shift);
+		s = round_down(s, 1 << bb->shift);
+		next = round_up(next, 1 << bb->shift);
 		sectors = next - s;
 	}
 
@@ -1071,8 +1071,8 @@ static bool _badblocks_clear(struct badblocks *bb, sector_t s, sector_t sectors)
 		 * isn't than to think a block is not bad when it is.
 		 */
 		target = s + sectors;
-		roundup(s, 1 << bb->shift);
-		rounddown(target, 1 << bb->shift);
+		s = round_up(s, 1 << bb->shift);
+		target = round_down(target, 1 << bb->shift);
 		sectors = target - s;
 	}
 
@@ -1307,8 +1307,8 @@ int badblocks_check(struct badblocks *bb, sector_t s, sector_t sectors,
 		/* round the start down, and the end up */
 		sector_t target = s + sectors;
 
-		rounddown(s, 1 << bb->shift);
-		roundup(target, 1 << bb->shift);
+		s = round_down(s, 1 << bb->shift);
+		target = round_up(target, 1 << bb->shift);
 		sectors = target - s;
 	}
 
-- 
2.43.0