From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752241AbdESK47 (ORCPT ); Fri, 19 May 2017 06:56:59 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:58892 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750828AbdESK44 (ORCPT ); Fri, 19 May 2017 06:56:56 -0400 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.220.161 X-Original-MAILFROM: byungchul.park@lge.com From: "Byungchul Park" To: "'Peter Zijlstra'" Cc: , , , , , , , , , , , References: <1489479542-27030-1-git-send-email-byungchul.park@lge.com> <1489479542-27030-6-git-send-email-byungchul.park@lge.com> <20170519080708.GG28017@X58A-UD3R> <20170519103025.zb5impbsek77ahwa@hirez.programming.kicks-ass.net> In-Reply-To: <20170519103025.zb5impbsek77ahwa@hirez.programming.kicks-ass.net> Subject: RE: [PATCH v6 05/15] lockdep: Implement crossrelease feature Date: Fri, 19 May 2017 19:56:53 +0900 Message-ID: <005a01d2d08e$9fe62800$dfb27800$@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQKHTxRKaSFn9YT2gkiC97K73S8y4AJVmGSqAXDKYtYC/1/6QKBcTcwQ Content-Language: ko Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Peter Zijlstra [mailto:peterz@infradead.org] > Sent: Friday, May 19, 2017 7:30 PM > To: Byungchul Park > Cc: mingo@kernel.org; tglx@linutronix.de; walken@google.com; > boqun.feng@gmail.com; kirill@shutemov.name; linux-kernel@vger.kernel.org; > linux-mm@kvack.org; iamjoonsoo.kim@lge.com; akpm@linux-foundation.org; > willy@infradead.org; npiggin@gmail.com; kernel-team@lge.com > Subject: Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature > > On Fri, May 19, 2017 at 05:07:08PM +0900, Byungchul Park wrote: > > On Tue, Mar 14, 2017 at 05:18:52PM +0900, Byungchul Park wrote: > > > Lockdep is a runtime locking correctness validator that detects and > > > reports a deadlock or its possibility by checking dependencies between > > > locks. It's useful since it does not report just an actual deadlock > but > > > also the possibility of a deadlock that has not actually happened yet. > > > That enables problems to be fixed before they affect real systems. > > > > > > However, this facility is only applicable to typical locks, such as > > > spinlocks and mutexes, which are normally released within the context > in > > > which they were acquired. However, synchronization primitives like > page > > > locks or completions, which are allowed to be released in any context, > > > also create dependencies and can cause a deadlock. So lockdep should > > > track these locks to do a better job. The 'crossrelease' > implementation > > > makes these primitives also be tracked. > > > > Excuse me but I have a question... > > > > Only for maskable irq, can I assume that hardirq are prevented within > > hardirq context? I remember that nested interrupts were allowed in the > > past but not recommanded. But what about now? I'm curious about the > > overall direction of kernel and current status. It would be very > > appriciated if you answer it. > > So you're right. In general enabling IRQs from hardirq context is > discouraged but allowed. However, if you were to do that with a lock > held that would instantly make lockdep report a deadlock, as the lock is > then both used from IRQ context and has IRQs enabled. > > So from a locking perspective you can assume no nesting, but from a > state tracking pov we have to deal with the nesting I think (although it > is very rare). Got it. Thank you. > You're asking this in relation to the rollback thing, right? I think we Exactly. I wanted to make it clear when implementing the rollback for irqs and works of workqueue. > should only save the state when hardirq_context goes from 0->1 and > restore on 1->0. Yes, it's already done in v6, as you are saying. Thank you very much.