linux-kernel - [PATCH] linux/log2.h: Fix roundup_pow_of

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Message-Id: <1449156616-11474-1-git-send-email-sasha.levin@oracle.com>
Date:	Thu,  3 Dec 2015 10:30:16 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, Sasha Levin <sasha.levin@...cle.com>
Subject: [PATCH] linux/log2.h: Fix roundup_pow_of_two(0)

Passing 0 to roundup_pow_of_two would lead to wrapping around and trying to
find the last set bit on (unsigned long)(-1), which is obviously wrong.

Instead, deal with this case by rounding it up to the closest power of two
(2 ** 0).

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
---
 include/linux/log2.h |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/log2.h b/include/linux/log2.h
index fd7ff3d..b6bdf0c 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -60,6 +60,9 @@ bool is_power_of_2(unsigned long n)
 static inline __attribute__((const))
 unsigned long __roundup_pow_of_two(unsigned long n)
 {
+	if (n == 0)
+		return 1UL << 0;
+
 	return 1UL << fls_long(n - 1);
 }
 
-- 
1.7.10.4

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