linux-kernel - [PATCH percpu/for-3.15] percpu: allocation size should be even

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Message-ID: <20140317201201.GD17373@mtj.dyndns.org>
Date:	Mon, 17 Mar 2014 16:12:01 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Stephen Tweedie <sct@...hat.com>,
	Jeremy Eder <jeder@...hat.com>
Subject: [PATCH percpu/for-3.15] percpu: allocation size should be even

>From 2f69fa829cb4ca062aaffee9ab9eb44484db75b1 Mon Sep 17 00:00:00 2001
From: Viro <viro@...IV.linux.org.uk>
Date: Mon, 17 Mar 2014 16:01:27 -0400

723ad1d90b56 ("percpu: store offsets instead of lengths in ->map[]")
updated percpu area allocator to use the lowest bit, instead of sign,
to signify whether the area is occupied and forced min align to 2;
unfortunately, it forgot to force the allocation size to be even
causing malfunctions for the very rare odd-sized allocations.

Always force the allocations to be even sized.

tj: Wrote patch description.

Original-patch-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Tejun Heo <tj@...nel.org>
---
Applied to percpu/for-3.15.

Thanks.

 mm/percpu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index c7206d0..202e104 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -713,11 +713,14 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved)
 
 	/*
 	 * We want the lowest bit of offset available for in-use/free
-	 * indicator.
+	 * indicator, so force >= 16bit alignment and make size even.
 	 */
 	if (unlikely(align < 2))
 		align = 2;
 
+	if (unlikely(size & 1))
+		size++;
+
 	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
 		WARN(true, "illegal size (%zu) or align (%zu) for "
 		     "percpu allocation\n", size, align);
-- 
1.8.5.3

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