Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756527Ab1FUADj (ORCPT ); Mon, 20 Jun 2011 20:03:39 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:44508 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756391Ab1FUADg (ORCPT ); Mon, 20 Jun 2011 20:03:36 -0400 Date: Mon, 20 Jun 2011 17:02:49 -0700 From: Andrew Morton To: H Hartley Sweeten Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "benh@kernel.crashing.org" , "yinghai@kernel.org" , "hpa@linux.intel.com" , Pekka Enberg Subject: Re: [Q] mm/memblock.c: cast truncates bits from RED_INACTIVE Message-Id: <20110620170249.d5cd98b1.akpm@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3347 Lines: 93 On Tue, 14 Jun 2011 19:47:19 -0500 H Hartley Sweeten wrote: > Hello all, > > Sparse is reporting a couple warnings in mm/memblock.c: > > warning: cast truncates bits from constant value (9f911029d74e35b becomes 9d74e35b) > > The warnings are due to the cast of RED_INACTIVE in memblock_analyze(): > > /* Check marker in the unused last array entry */ > WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base > != (phys_addr_t)RED_INACTIVE); > WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base > != (phys_addr_t)RED_INACTIVE); > > And in memblock_init(): > > /* Write a marker in the unused last array entry */ > memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE; > memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE; > > Could this cause any problems? If not, is there anyway to quiet the sparse noise? > It's all just a debugging check and that check will continue to work OK despite this bug. But yes, it's ugly and should be fixed. I don't think that mm/memblock.c should have reused RED_INACTIVE. That's a slab thing and wedging it into a phys_addr_t was inappropriate. In fact I don't think RED_INACTIVE should exist. It's just inviting other subsystems to (ab)use it. It should be replaced by a slab-specific SLAB_RED_INACTIVE, as slub did with SLUB_RED_INACTIVE. I'd suggest something like the below, which I didn't test. Feel free to send it back at me, or ignore it ;) diff -puN include/linux/poison.h~a include/linux/poison.h --- a/include/linux/poison.h~a +++ a/include/linux/poison.h @@ -40,6 +40,12 @@ #define RED_INACTIVE 0x09F911029D74E35BULL /* when obj is inactive */ #define RED_ACTIVE 0xD84156C5635688C0ULL /* when obj is active */ +#ifdef CONFIG_PHYS_ADDR_T_64BIT +#define MEMBLOCK_INACTIVE 0x3a84fb0144c9e71bULL +#else +#define MEMBLOCK_INACTIVE 0x44c9e71bUL +#endif + #define SLUB_RED_INACTIVE 0xbb #define SLUB_RED_ACTIVE 0xcc diff -puN mm/memblock.c~a mm/memblock.c --- a/mm/memblock.c~a +++ a/mm/memblock.c @@ -758,9 +758,9 @@ void __init memblock_analyze(void) /* Check marker in the unused last array entry */ WARN_ON(memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS].base - != (phys_addr_t)RED_INACTIVE); + != MEMBLOCK_INACTIVE); WARN_ON(memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS].base - != (phys_addr_t)RED_INACTIVE); + != MEMBLOCK_INACTIVE); memblock.memory_size = 0; @@ -786,8 +786,8 @@ void __init memblock_init(void) memblock.reserved.max = INIT_MEMBLOCK_REGIONS; /* Write a marker in the unused last array entry */ - memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE; - memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = (phys_addr_t)RED_INACTIVE; + memblock.memory.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE; + memblock.reserved.regions[INIT_MEMBLOCK_REGIONS].base = MEMBLOCK_INACTIVE; /* Create a dummy zero size MEMBLOCK which will get coalesced away later. * This simplifies the memblock_add() code below... _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/