linux-kernel - [PATCH v2 1/2] memblock: add assertion for zero allocation alignment

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Date:	Fri, 22 Feb 2013 01:40:21 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2 1/2] memblock: add assertion for zero allocation alignment

This came to light when calling memblock allocator from arc port (for
copying flattended DT). If a "0" alignment is passed, the allocator
round_up() call incorrectly rounds up the size to 0.

round_up(num, alignto) => ((num - 1) | (alignto -1)) + 1

While the obvious allocation failure causes kernel to panic, it is
better to warn the caller to fix the code.

Tejun suggested that instead of BUG_ON(!align) - which might be
ineffective due to pending console init and such, it is better to
WARN_ON, and continue the boot with a reasonable default align.

Caller passing @size need not be handled similarly as the subsequent
panic will indicate that anyhow.

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/memblock.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 1bcd9b9..f3804bd 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -824,6 +824,9 @@ static phys_addr_t __init memblock_alloc_base_nid(phys_addr_t size,
 	/* align @size to avoid excessive fragmentation on reserved array */
 	size = round_up(size, align);
 
+	if (WARN_ON(!align))
+		align = __alignof__(long long);
+
 	found = memblock_find_in_range_node(0, max_addr, size, align, nid);
 	if (found && !memblock_reserve(found, size))
 		return found;
-- 
1.7.4.1

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