On 4/6/23 08:10, Kirill A. Shutemov wrote:
On Thu, Apr 06, 2023 at 06:57:41AM -0700, Guenter Roeck wrote:
On 4/6/23 00:25, Kirill A. Shutemov wrote:
On Wed, Apr 05, 2023 at 10:20:26PM -0700, Guenter Roeck wrote:
Hi,
On Wed, Mar 15, 2023 at 06:38:00PM +0300, Kirill A. Shutemov wrote:
fix min() warning
Link: https://lkml.kernel.org/r/20230315153800.32wib3n5rickolvh@box
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Link: https://lore.kernel.org/oe-kbuild-all/202303152343.D93IbJmn-lkp@xxxxxxxxx/
Signed-off-by: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
This patch results in various boot failures (hang) on arm targets
in linux-next. Debug messages reveal the reason.
########### MAX_ORDER=10 start=0 __ffs(start)=-1 min()=10 min_t=-1
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If start==0, __ffs(start) returns 0xfffffff or (as int) -1, which min_t()
interprets as such, while min() apparently uses the returned unsigned long
value. Obviously a negative order isn't received well by the rest of the
code.
Actually, __ffs() is not defined for 0.
Maybe something like this?
diff --git a/mm/memblock.c b/mm/memblock.c
index 7911224b1ed3..63603b943bd0 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2043,7 +2043,11 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
int order;
while (start < end) {
- order = min_t(int, MAX_ORDER, __ffs(start));
+ /* __ffs() behaviour is undefined for 0 */
+ if (start)
+ order = min_t(int, MAX_ORDER, __ffs(start));
+ else
+ order = MAX_ORDER;
Shouldn't that be
else
order = 0;
?
+Mike.
No. start == 0 is MAX_ORDER-aligned. We want to free the pages in the
largest chunks alignment allows.
Ah, ok. Makes sense.
Thanks,
Guenter
