From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752872Ab3GFIKl (ORCPT ); Sat, 6 Jul 2013 04:10:41 -0400 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:49497 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752667Ab3GFIKh (ORCPT ); Sat, 6 Jul 2013 04:10:37 -0400 Message-ID: <51D7D003.2030001@linux.vnet.ibm.com> Date: Sat, 06 Jul 2013 13:36:27 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Wang YanQing , xiaoguangrong@cn.fujitsu.com, mingo@elte.hu, paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, npiggin@suse.de, deepthi@linux.vnet.ibm.com, peterz@infradead.org, rusty@rustcorp.com.au, heiko.carstens@de.ibm.com, rostedt@goodmis.org, miltonm@bga.com, srivatsa.bhat@linux.vnet.ibm.com, jens.axboe@oracle.com, tj@kernel.org, akpm@linux-foundation.org, svaidy@linux.vnet.ibm.com, shli@kernel.org, tglx@linutronix.de, lig.fnst@cn.fujitsu.com, anton@samba.org Subject: Re: [PATCH 3/3] smp/ipi:Remove check around csd lock in handler for smp_call_function variants References: <20130705162548.16888.18957.stgit@preeti.in.ibm.com> <20130705162720.16888.81958.stgit@preeti.in.ibm.com> <20130706054552.GA2929@udknight> In-Reply-To: <20130706054552.GA2929@udknight> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13070608-5564-0000-0000-000008AD656B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/06/2013 11:15 AM, Wang YanQing wrote: > On Fri, Jul 05, 2013 at 09:57:21PM +0530, Preeti U Murthy wrote: >> call_single_data is always locked by all callers of >> arch_send_call_function_single_ipi() or >> arch_send_call_function_ipi_mask() which results in execution of >> generic_call_function_interrupt() handler. >> >> Hence remove the check for lock on csd in generic_call_function_interrupt() >> handler, before unlocking it. > > I can't find where is the generic_call_function_interrupt :) Sorry about this error :) > >> Signed-off-by: Preeti U Murthy >> Cc: Peter Zijlstra >> Cc: Ingo Molnar >> Cc: Xiao Guangrong >> Cc: srivatsa.bhat@linux.vnet.ibm.com >> Cc: Paul E. McKenney >> Cc: Steven Rostedt >> Cc: Rusty Russell > --- >> >> kernel/smp.c | 14 +------------- >> 1 file changed, 1 insertion(+), 13 deletions(-) >> >> diff --git a/kernel/smp.c b/kernel/smp.c >> index b6981ae..d37581a 100644 >> --- a/kernel/smp.c >> +++ b/kernel/smp.c >> @@ -181,25 +181,13 @@ void generic_smp_call_function_single_interrupt(void) >> >> while (!list_empty(&list)) { >> struct call_single_data *csd; >> - unsigned int csd_flags; >> >> csd = list_entry(list.next, struct call_single_data, list); >> list_del(&csd->list); >> >> - /* >> - * 'csd' can be invalid after this call if flags == 0 >> - * (when called through generic_exec_single()), >> - * so save them away before making the call: >> - */ >> - csd_flags = csd->flags; >> - > > You haven't mention this change in the ChangeLog, don't do it. Right, I will include it in the changelog. > I can't see any harm to remove csd_flags, but I hope others > check it again. > >> csd->func(csd->info); >> >> - /* >> - * Unlocked CSDs are valid through generic_exec_single(): >> - */ >> - if (csd_flags & CSD_FLAG_LOCK) >> - csd_unlock(csd); >> + csd_unlock(csd); > > I don't like this change, I think check CSD_FLAG_LOCK > to make sure we really need csd_unlock is good. Ideally it should be under a WARN_ON(). csd_unlock() has that WARN_ON(). Unlocking a parameter which is not locked should be seen as a bug, which the above code is not doing. In fact it avoids it being reported as a bug. > > Just like you can't know who and how people will use the > API, so some robust check code is good. > Regards Preeti U Murthy