From: Matthew Wilcox (Oracle) <willy@infradead.org>
Date: Mon, 29 Apr 2024 14:47:51 +0000 (+0100)
Subject: bounds: Use the right number of bits for power-of-two CONFIG_NR_CPUS
X-Git-Tag: v6.9-rc7~37
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=5af385f5f4cddf908f663974847a4083b2ff2c79;p=linux-block.git

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

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@rosalinux.ru>
Tested-by: Ильфат Гаптрахманов <i.gaptrakhmanov@rosalinux.ru>
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/3347
Link: https://lore.kernel.org/all/1c978cf1-2934-4e66-e4b3-e81b04cb3571@rosalinux.ru/
Fixes: f2d5dcb48f7b (bounds: support non-power-of-two CONFIG_NR_CPUS)
Cc:  <stable@vger.kernel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/kernel/bounds.c b/kernel/bounds.c
index c5a9fcd2d622..29b2cd00df2c 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, order_base_2(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
 #ifdef CONFIG_LRU_GEN