From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vineet Gupta Subject: Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long Date: Mon, 9 Jul 2018 11:27:31 -0700 Message-ID: References: <20180709044444.6397-1-abrodkin@synopsys.com> <91c57eeba2134dd99a9f0e11fa883c7c@AcuMS.aculab.com> <82d2b36fa913bca6d56c7bf32a653324970817b8.camel@synopsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <82d2b36fa913bca6d56c7bf32a653324970817b8.camel@synopsys.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Alexey Brodkin , "David.Laight@ACULAB.COM" Cc: "linux-arch@vger.kernel.org" , "greg@kroah.com" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , "gregkh@linuxfoundation.org" , "tglx@linutronix.de" , "linux-snps-arc@lists.infradead.org" List-Id: linux-arch.vger.kernel.org On 07/09/2018 03:23 AM, Alexey Brodkin wrote: > Hi David, > > On Mon, 2018-07-09 at 10:18 +0000, David Laight wrote: >> From: Alexey Brodkin >>> Sent: 09 July 2018 11:00 >> >> ... >>> That's a good idea indeed but it doesn't solve the problem with >>> struct devres_node. Consider the following snippet: >>> -------------------------------->8------------------------------- >>> struct mystruct { >>> atomic64_t myvar; >>> } >>> >>> struct mystruct *p; >>> p = devm_kzalloc(dev, sizeof(*p), GFP_KERNEL); >>> -------------------------------->8------------------------------- >>> >>> Here myvar address will match address of "data" member of struct devres_node. >>> So if "data" is has offset of 12 bytes from the beginning of a page then >>> myvar won't be 64-bit aligned regardless of myvar's attribute, right? >> >> ... >>>>> - unsigned long long data[]; /* guarantee ull alignment */ >> >> Ahh, that line should be: >> u8 data[] __aligned(8); /* Guarantee 64bit alignment */ > > And that pretty much what I suggested in my initial patch :) > > For the record x86 has exactly the same atomic64_t as you suggested, > see https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/atomic64_32.h#L13: > ---------------------->8------------------ > typedef struct { > u64 __aligned(8) counter; > } atomic64_t; > ---------------------->8------------------ And so does the ARC version since when the atomic64_t support was added by commit ce6365270ecd Also, you should consider using the pre-canned type aligned_u64. typedef struct { aligned_u64 counter; ^^^^^^^^^^^ } atomic64_t; From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtprelay.synopsys.com ([198.182.60.111]:57904 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754516AbeGIS1m (ORCPT ); Mon, 9 Jul 2018 14:27:42 -0400 Subject: Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long References: <20180709044444.6397-1-abrodkin@synopsys.com> <91c57eeba2134dd99a9f0e11fa883c7c@AcuMS.aculab.com> <82d2b36fa913bca6d56c7bf32a653324970817b8.camel@synopsys.com> From: Vineet Gupta Message-ID: Date: Mon, 9 Jul 2018 11:27:31 -0700 MIME-Version: 1.0 In-Reply-To: <82d2b36fa913bca6d56c7bf32a653324970817b8.camel@synopsys.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Alexey Brodkin , "David.Laight@ACULAB.COM" Cc: "linux-arch@vger.kernel.org" , "greg@kroah.com" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , "gregkh@linuxfoundation.org" , "tglx@linutronix.de" , "linux-snps-arc@lists.infradead.org" Message-ID: <20180709182731.-SqIukdb6Hiucjgme_hQKQdKGtvYMQxaQEPF6wf1N2I@z> On 07/09/2018 03:23 AM, Alexey Brodkin wrote: > Hi David, > > On Mon, 2018-07-09 at 10:18 +0000, David Laight wrote: >> From: Alexey Brodkin >>> Sent: 09 July 2018 11:00 >> >> ... >>> That's a good idea indeed but it doesn't solve the problem with >>> struct devres_node. Consider the following snippet: >>> -------------------------------->8------------------------------- >>> struct mystruct { >>> atomic64_t myvar; >>> } >>> >>> struct mystruct *p; >>> p = devm_kzalloc(dev, sizeof(*p), GFP_KERNEL); >>> -------------------------------->8------------------------------- >>> >>> Here myvar address will match address of "data" member of struct devres_node. >>> So if "data" is has offset of 12 bytes from the beginning of a page then >>> myvar won't be 64-bit aligned regardless of myvar's attribute, right? >> >> ... >>>>> - unsigned long long data[]; /* guarantee ull alignment */ >> >> Ahh, that line should be: >> u8 data[] __aligned(8); /* Guarantee 64bit alignment */ > > And that pretty much what I suggested in my initial patch :) > > For the record x86 has exactly the same atomic64_t as you suggested, > see https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/atomic64_32.h#L13: > ---------------------->8------------------ > typedef struct { > u64 __aligned(8) counter; > } atomic64_t; > ---------------------->8------------------ And so does the ARC version since when the atomic64_t support was added by commit ce6365270ecd Also, you should consider using the pre-canned type aligned_u64. typedef struct { aligned_u64 counter; ^^^^^^^^^^^ } atomic64_t;