From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933587AbeBVRl6 (ORCPT ); Thu, 22 Feb 2018 12:41:58 -0500 Received: from merlin.infradead.org ([205.233.59.134]:55770 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933427AbeBVRl5 (ORCPT ); Thu, 22 Feb 2018 12:41:57 -0500 Date: Thu, 22 Feb 2018 18:41:53 +0100 From: Peter Zijlstra To: Boqun Feng Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrea Parri Subject: Re: [RFC tip/locking/lockdep v5 08/17] lockdep: Fix recursive read lock related safe->unsafe detection Message-ID: <20180222174153.GV25201@hirez.programming.kicks-ass.net> References: <20180222070904.548-1-boqun.feng@gmail.com> <20180222070904.548-9-boqun.feng@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180222070904.548-9-boqun.feng@gmail.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 22, 2018 at 03:08:55PM +0800, Boqun Feng wrote: > There are four cases for recursive read lock realted deadlocks: > > (--(X..Y)--> means a strong dependency path starts with a --(X*)--> > dependency and ends with a --(*Y)-- dependency.) > > 1. An irq-safe lock L1 has a dependency --(*..*)--> to an > irq-unsafe lock L2. > > 2. An irq-read-safe lock L1 has a dependency --(N..*)--> to an > irq-unsafe lock L2. > > 3. An irq-safe lock L1 has a dependency --(*..N)--> to an > irq-read-unsafe lock L2. > > 4. An irq-read-safe lock L1 has a dependency --(N..N)--> to an > irq-read-unsafe lock L2. > > The current check_usage() only checks 1) and 2), so this patch adds > checks for 3) and 4) and makes sure when find_usage_{back,for}wards find > an irq-read-{,un}safe lock, the traverse path should ends at a > dependency --(*N)-->. Note when we search backwards, --(*N)--> indicates > a real dependency --(N*)-->. > > Signed-off-by: Boqun Feng > --- > kernel/locking/lockdep.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 0b0ad3db78b4..bd3eef664f9d 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1504,7 +1504,14 @@ check_redundant(struct lock_list *root, struct held_lock *target, > > static inline int usage_match(struct lock_list *entry, void *bit) > { > - return entry->class->usage_mask & (1 << (enum lock_usage_bit)bit); > + enum lock_usage_bit ub = (enum lock_usage_bit)bit; > + > + > + if (ub & 1) > + return entry->class->usage_mask & (1 << ub) && > + !entry->is_rr; > + else > + return entry->class->usage_mask & (1 << ub); > } The whole is_rr/have_xr thing and backwards hurts my brain. That really wants more than a little 'Note'. Also, the above is unreadable, something like: unsigned long usage_mask = entry->class->usage_mask; enum lock_usage_bit ub = (enum lock_usage_bit)bit; unsigned long mask = 1ULL << ub; if (ub & 1) /* __STATE_RR */ return !entry->have_xr && (usage_mask & mask); return !!(usage_mask & mask); maybe. Also, perhaps we should make __bfs(.match) have a bool return value.