From 59f876fb9d68a4d8c20305d7a7a0daf4ee9478a8 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Thu, 6 Apr 2023 10:25:29 +0300 Subject: mm: avoid passing 0 to __ffs() 23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely") results in various boot failures (hang) on arm targets 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. [akpm@linux-foundation.org: fix comment, per Mike] Link: https://lkml.kernel.org/r/ZDBa7HWZK69dKKzH@kernel.org Link: https://lkml.kernel.org/r/20230406072529.vupqyrzqnhyozeyh@box.shutemov.name Fixes: 23baf831a32c ("mm, treewide: redefine MAX_ORDER sanely") Signed-off-by: "Kirill A. Shutemov" Reported-by: Guenter Roeck Link: https://lkml.kernel.org/r/9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net Reviewed-by: Mike Rapoport (IBM) Signed-off-by: Andrew Morton --- mm/memblock.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'mm/memblock.c') diff --git a/mm/memblock.c b/mm/memblock.c index 7911224b1ed3..3feafea06ab2 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -2043,7 +2043,16 @@ 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)); + /* + * Free the pages in the largest chunks alignment allows. + * + * __ffs() behaviour is undefined for 0. start == 0 is + * MAX_ORDER-aligned, set order to MAX_ORDER for the case. + */ + if (start) + order = min_t(int, MAX_ORDER, __ffs(start)); + else + order = MAX_ORDER; while (start + (1UL << order) > end) order--; -- cgit v1.2.3