linux-kernel - [PATCH] workqueue: Fix alignment calculation in alloc

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Message-ID: <20101025212706.27798.23957.stgit@warthog.procyon.org.uk>
Date:	Mon, 25 Oct 2010 22:27:06 +0100
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...l.org, akpm@...ux-foundation.org
Cc:	Tejun Heo <tj@...nel.org>, linux-am33-list@...hat.com,
	linux-kernel@...r.kernel.org,
	Akira Takeuchi <takeuchi.akr@...panasonic.com>,
	Mark Salter <msalter@...hat.com>
Subject: [PATCH] workqueue: Fix alignment calculation in alloc_cwqs()

In the MN10300 arch, we occasionally see an assertion being tripped in
alloc_cwqs() at the following line:

	/* just in case, make sure it's actually aligned */
  --->	BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
	return wq->cpu_wq.v ? 0 : -ENOMEM;

The values are:

	wa->cpu_wq.v => 0x902776e0
	align => 0x100

and align is calculated by the following:

	const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
				   __alignof__(unsigned long long));

which is wrong.  __alignof__() returns its value in bytes, but:

	1 << WORK_STRUCT_FLAG_BITS

returns the value in bits.  It needs dividing by the number of bits in a byte.

Reported-by: Akira Takeuchi <takeuchi.akr@...panasonic.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Mark Salter <msalter@...hat.com>
cc: Tejun Heo <tj@...nel.org>
---

 kernel/workqueue.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)


diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 30acdb7..e29ebd4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2766,8 +2766,9 @@ static int alloc_cwqs(struct workqueue_struct *wq)
 	 * unsigned long long.
 	 */
 	const size_t size = sizeof(struct cpu_workqueue_struct);
-	const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
-				   __alignof__(unsigned long long));
+	const size_t align =
+		max_t(size_t, 1 << (WORK_STRUCT_FLAG_BITS - BITS_PER_BYTE),
+		      __alignof__(unsigned long long));
 #ifdef CONFIG_SMP
 	bool percpu = !(wq->flags & WQ_UNBOUND);
 #else

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