diff options
| author | Kirill A. Shutemov <kirill@shutemov.name> | 2023-04-06 10:25:29 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-04-18 16:29:42 -0700 |
| commit | 59f876fb9d68a4d8c20305d7a7a0daf4ee9478a8 (patch) | |
| tree | 4b4d6b6bfd75ea2623b77598ca8fa445a027b526 /mm/memory_hotplug.c | |
| parent | f8f238ffe5e96a924a2ddbbaa872231fbf2c0d7b (diff) | |
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" <kirill@shutemov.name>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lkml.kernel.org/r/9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memory_hotplug.c')
| -rw-r--r-- | mm/memory_hotplug.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index c8f0a8c2d049..8e0fa209d533 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -605,7 +605,18 @@ static void online_pages_range(unsigned long start_pfn, unsigned long nr_pages) * this and the first chunk to online will be pageblock_nr_pages. */ for (pfn = start_pfn; pfn < end_pfn;) { - int order = min_t(int, MAX_ORDER, __ffs(pfn)); + int order; + + /* + * Free to online 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 (pfn) + order = min_t(int, MAX_ORDER, __ffs(pfn)); + else + order = MAX_ORDER; (*online_page_callback)(pfn_to_page(pfn), order); pfn += (1UL << order); |