[PATCH] bounds: Use the right number of bits for power-of-two CONFIG_NR_CPUS

[Matthew Wilcox (Oracle)]

bits_per() rounds up to the next power of two when passed a power of
two.  This causes crashes on some machines and configurations.

Reported-by: Михаил Новоселов <m.novosyolov@xxxxxxxxxxxx>
Tested-by: Ильфат Гаптрахманов <i.gaptrakhmanov@xxxxxxxxxxxx>
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/3347
Link: https://lore.kernel.org/all/1c978cf1-2934-4e66-e4b3-e81b04cb3571@xxxxxxxxxxxx/
Fixes: f2d5dcb48f7b (bounds: support non-power-of-two CONFIG_NR_CPUS)
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 kernel/bounds.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bounds.c b/kernel/bounds.c
index c5a9fcd2d622..8553368ccf79 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -19,7 +19,7 @@ int main(void)
 	DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
 	DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
 #ifdef CONFIG_SMP
-	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS));
+	DEFINE(NR_CPUS_BITS, bits_per(CONFIG_NR_CPUS - 1));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 #ifdef CONFIG_LRU_GEN
-- 
2.43.0