Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752982AbbDGK31 (ORCPT ); Tue, 7 Apr 2015 06:29:27 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:49720 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750983AbbDGK3Z (ORCPT ); Tue, 7 Apr 2015 06:29:25 -0400 Date: Tue, 7 Apr 2015 12:29:12 +0200 From: Peter Zijlstra To: Mike Galbraith Cc: Steven Rostedt , Thavatchai Makphaibulchoke , linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, linux-rt-users@vger.kernel.org, Sebastian Andrzej Siewior Subject: Re: [PATCH v2 1/2] rtmutex Real-Time Linux: Fixing kernel BUG at kernel/locking/rtmutex.c:997! Message-ID: <20150407102912.GK23123@twins.programming.kicks-ass.net> References: <1424395866-81589-1-git-send-email-tmac@hp.com> <1428369962-74723-1-git-send-email-tmac@hp.com> <1428369962-74723-2-git-send-email-tmac@hp.com> <20150406215959.4e8ad37b@grimm.local.home> <1428383383.3152.5.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1428383383.3152.5.camel@gmail.com> 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 Content-Length: 1993 Lines: 52 On Tue, Apr 07, 2015 at 07:09:43AM +0200, Mike Galbraith wrote: > On Mon, 2015-04-06 at 21:59 -0400, Steven Rostedt wrote: > > > > We really should have a rt_spin_trylock_in_irq() and not have the > > below if conditional. > > > > The paths that will be executed in hard irq context are static. They > > should be labeled as such. > > +/* > + * Special purpose for locks taken in interrupt context: Take and hold > + * ->wait_lock lest PI catching us with our fingers in the cookie jar. > + * Do NOT abuse. > + */ > +int __lockfunc rt_spin_trylock_in_irq(spinlock_t *lock) > +{ > + struct task_struct *owner; > + if (!raw_spin_trylock(&lock->lock.wait_lock)) > + return 0; > + owner = idle_task(raw_smp_processor_id()); > + if (!(rt_mutex_cmpxchg(&lock->lock, NULL, owner))) { > + raw_spin_unlock(&lock->lock.wait_lock); > + return 0; > + } > + spin_acquire(&lock->dep_map, 0, 1, _RET_IP_); > + return 1; > +} > + > +/* ONLY for use with rt_spin_trylock_in_irq(), do NOT abuse. */ > +void __lockfunc rt_spin_trylock_in_irq_unlock(spinlock_t *lock) > +{ > + struct task_struct *owner = idle_task(raw_smp_processor_id()); > + /* NOTE: we always pass in '1' for nested, for simplicity */ > + spin_release(&lock->dep_map, 1, _RET_IP_); > + BUG_ON(!(rt_mutex_cmpxchg(&lock->lock, owner, NULL))); > + raw_spin_unlock(&lock->lock.wait_lock); > +} > + Can someone explain this braindamage? You should _NOT_ take mutexes in hardirq context. And if its an irq thread, then the irq thread _IS_ the right owner, the thread needs to be boosted by waiters. The idle thread cannot ever be owner of a mutex, that's complete and utter bullshit. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/