From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: Re: [PATCH v5 05/45] percpu_rwlock: Make percpu-rwlocks IRQ-safe, optimally Date: Mon, 11 Feb 2013 00:57:25 +0530 Message-ID: <5117F49D.2030509@linux.vnet.ibm.com> References: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> <20130122073400.13822.52336.stgit@srivatsabhat.in.ibm.com> <20130208234403.GL2666@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from e28smtp01.in.ibm.com ([122.248.162.1]:49306 "EHLO e28smtp01.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755486Ab3BJT32 (ORCPT ); Sun, 10 Feb 2013 14:29:28 -0500 Received: from /spool/local by e28smtp01.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 11 Feb 2013 00:56:59 +0530 In-Reply-To: <20130208234403.GL2666@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: paulmck@linux.vnet.ibm.com Cc: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, fweisbec@gmail.com, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org On 02/09/2013 05:14 AM, Paul E. McKenney wrote: > On Tue, Jan 22, 2013 at 01:04:11PM +0530, Srivatsa S. Bhat wrote: >> If interrupt handlers can also be readers, then one of the ways to make >> per-CPU rwlocks safe, is to disable interrupts at the reader side before >> trying to acquire the per-CPU rwlock and keep it disabled throughout the >> duration of the read-side critical section. [...] >> -void percpu_read_lock(struct percpu_rwlock *pcpu_rwlock) >> +void percpu_read_lock_irqsafe(struct percpu_rwlock *pcpu_rwlock) >> { >> preempt_disable(); >> >> /* First and foremost, let the writer know that a reader is active */ >> - this_cpu_inc(*pcpu_rwlock->reader_refcnt); >> + this_cpu_add(*pcpu_rwlock->reader_refcnt, READER_PRESENT); >> >> /* >> * If we are already using per-cpu refcounts, it is not safe to switch >> * the synchronization scheme. So continue using the refcounts. >> */ >> if (reader_nested_percpu(pcpu_rwlock)) { >> - goto out; >> + this_cpu_inc(*pcpu_rwlock->reader_refcnt); > > Hmmm... If the reader is nested, it -doesn't- need the memory barrier at > the end of this function. If there is lots of nesting, it might be > worth getting rid of it. > Yes, good point! Will get rid of it. Regards, Srivatsa S. Bhat