From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id E9D1790013A for ; Tue, 21 Jun 2011 01:49:19 -0400 (EDT) Message-ID: <4E0030DB.6000208@cs.helsinki.fi> Date: Tue, 21 Jun 2011 08:49:15 +0300 From: Pekka Enberg MIME-Version: 1.0 Subject: Re: [Q] mm/memblock.c: cast truncates bits from RED_INACTIVE References: <20110620170249.d5cd98b1.akpm@linux-foundation.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: H Hartley Sweeten Cc: Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "benh@kernel.crashing.org" , "yinghai@kernel.org" , "hpa@linux.intel.com" On 6/21/11 3:31 AM, H Hartley Sweeten wrote: > On Monday, June 20, 2011 5:03 PM, Andrew Morton wrote: >> 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... > > FWIW, your patch above quiet's the sparse warnings on my system (arm ep93xx) and > the system boots and runs fine. > > If you want it.. > > Tested-by: H Hartley Sweeten Acked-by: Pekka Enberg -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org