From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx183.postini.com [74.125.245.183]) by kanga.kvack.org (Postfix) with SMTP id 6B3046B0002 for ; Thu, 21 Feb 2013 15:48:57 -0500 (EST) Message-ID: <512687F9.8090000@synopsys.com> Date: Fri, 22 Feb 2013 02:17:53 +0530 From: Vineet Gupta MIME-Version: 1.0 Subject: Re: [PATCH v2 1/2] memblock: add assertion for zero allocation alignment References: <20130221193639.GN3570@htj.dyndns.org> <1361477421-3964-1-git-send-email-vgupta@synopsys.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Yinghai Lu Cc: Tejun Heo , Andrew Morton , Wanpeng Li , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Friday 22 February 2013 02:01 AM, Yinghai Lu wrote: > On Thu, Feb 21, 2013 at 12:10 PM, Vineet Gupta > wrote: >> 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 >> Cc: Andrew Morton >> Cc: Tejun Heo >> Cc: Yinghai Lu >> Cc: Wanpeng Li >> Cc: Ingo Molnar >> Cc: linux-mm@kvack.org >> Cc: linux-kernel@vger.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); >> + > the checking should be put before round_up? Oops my bad. Interestingly however, I did test this exact patch on ARC before sending out - passing @align = 0 to make it hit the WARN. It prints the warning, and uses @size=0, @align=8 for memblock_find_in_range_node() and successfully allocates memory as opposed to failure for @size=0, @align=0 scenario. This is kind of weird. Anyhow I'll send the updated patch to fix the gotcha ! Thx, -Vineet -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org