From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Date: Wed, 30 Mar 2016 13:25:49 +0000 Subject: Re: [PATCH 03/11] locking, rwsem: introduce basis for down_write_killable Message-Id: <20160330132549.GU3408@twins.programming.kicks-ass.net> List-Id: References: <1456750705-7141-1-git-send-email-mhocko@kernel.org> <1456750705-7141-4-git-send-email-mhocko@kernel.org> In-Reply-To: <1456750705-7141-4-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko On Mon, Feb 29, 2016 at 01:58:17PM +0100, Michal Hocko wrote: > @@ -215,16 +216,34 @@ void __sched __down_write(struct rw_semaphore *sem) > */ > if (sem->count = 0) > break; > - set_task_state(tsk, TASK_UNINTERRUPTIBLE); > + set_task_state(tsk, state); > raw_spin_unlock_irqrestore(&sem->wait_lock, flags); > schedule(); > + if (signal_pending_state(state, current)) { > + ret = -EINTR; > + raw_spin_lock_irqsave(&sem->wait_lock, flags); > + goto out; > + } > raw_spin_lock_irqsave(&sem->wait_lock, flags); > } > /* got the lock */ > sem->count = -1; > @@ -487,20 +488,38 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) > /* Block until there are no active lockers. */ > do { > schedule(); > - set_current_state(TASK_UNINTERRUPTIBLE); > + if (signal_pending_state(state, current)) { > + raw_spin_lock_irq(&sem->wait_lock); > + ret = ERR_PTR(-EINTR); > + goto out; > + } > + set_current_state(state); > } while ((count = sem->count) & RWSEM_ACTIVE_MASK); > > raw_spin_lock_irq(&sem->wait_lock); > } > __set_current_state(TASK_RUNNING); Why is the signal_pending_state() test _after_ the call to schedule() and before the 'trylock'. __mutex_lock_common() has it before the call to schedule and after the 'trylock'. The difference is that rwsem will now respond to the KILL and return -EINTR even if the lock is available, whereas mutex will acquire it and ignore the signal (for a little while longer). Neither is wrong per se, but I feel all the locking primitives should behave in a consistent manner in this regard. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753770AbcC3N0I (ORCPT ); Wed, 30 Mar 2016 09:26:08 -0400 Received: from casper.infradead.org ([85.118.1.10]:47512 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753391AbcC3N0F (ORCPT ); Wed, 30 Mar 2016 09:26:05 -0400 Date: Wed, 30 Mar 2016 15:25:49 +0200 From: Peter Zijlstra To: Michal Hocko Cc: LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko Subject: Re: [PATCH 03/11] locking, rwsem: introduce basis for down_write_killable Message-ID: <20160330132549.GU3408@twins.programming.kicks-ass.net> References: <1456750705-7141-1-git-send-email-mhocko@kernel.org> <1456750705-7141-4-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1456750705-7141-4-git-send-email-mhocko@kernel.org> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 29, 2016 at 01:58:17PM +0100, Michal Hocko wrote: > @@ -215,16 +216,34 @@ void __sched __down_write(struct rw_semaphore *sem) > */ > if (sem->count == 0) > break; > - set_task_state(tsk, TASK_UNINTERRUPTIBLE); > + set_task_state(tsk, state); > raw_spin_unlock_irqrestore(&sem->wait_lock, flags); > schedule(); > + if (signal_pending_state(state, current)) { > + ret = -EINTR; > + raw_spin_lock_irqsave(&sem->wait_lock, flags); > + goto out; > + } > raw_spin_lock_irqsave(&sem->wait_lock, flags); > } > /* got the lock */ > sem->count = -1; > @@ -487,20 +488,38 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) > /* Block until there are no active lockers. */ > do { > schedule(); > - set_current_state(TASK_UNINTERRUPTIBLE); > + if (signal_pending_state(state, current)) { > + raw_spin_lock_irq(&sem->wait_lock); > + ret = ERR_PTR(-EINTR); > + goto out; > + } > + set_current_state(state); > } while ((count = sem->count) & RWSEM_ACTIVE_MASK); > > raw_spin_lock_irq(&sem->wait_lock); > } > __set_current_state(TASK_RUNNING); Why is the signal_pending_state() test _after_ the call to schedule() and before the 'trylock'. __mutex_lock_common() has it before the call to schedule and after the 'trylock'. The difference is that rwsem will now respond to the KILL and return -EINTR even if the lock is available, whereas mutex will acquire it and ignore the signal (for a little while longer). Neither is wrong per se, but I feel all the locking primitives should behave in a consistent manner in this regard.