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

commit 5af385f upstream.

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 <[email protected]>
Tested-by: Ильфат Гаптрахманов <[email protected]>
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/3347
Link: https://lore.kernel.org/all/[email protected]/
Fixes: f2d5dcb (bounds: support non-power-of-two CONFIG_NR_CPUS)
Cc:  <[email protected]>
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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, order_base_2(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 	/* End of constants */