linux-kernel - [PATCH] bounds: Use the right number of bits for power-of-two CONFIG_NR

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Message-ID: <20240429144807.3012361-1-willy@infradead.org>
Date: Mon, 29 Apr 2024 15:47:51 +0100
From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Михаил Новоселов <m.novosyolov@...alinux.ru>,
	Ильфат Гаптрахманов <i.gaptrakhmanov@...alinux.ru>,
	stable@...r.kernel.org,
	Rik van Riel <riel@...riel.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] 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@...alinux.ru>
Tested-by: Ильфат Гаптрахманов <i.gaptrakhmanov@...alinux.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@...r.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 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