From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751452AbdJEOSq (ORCPT ); Thu, 5 Oct 2017 10:18:46 -0400 Received: from mx0a-00010702.pphosted.com ([148.163.156.75]:42936 "EHLO mx0b-00010702.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751323AbdJEOSo (ORCPT ); Thu, 5 Oct 2017 10:18:44 -0400 Date: Thu, 5 Oct 2017 09:17:44 -0500 From: Julia Cartwright To: Arnaldo Carvalho de Melo CC: , , , Arnaldo Carvalho de Melo , Clark Williams , Dean Luick , Dennis Dalessandro , Doug Ledford , Kaike Wan , Leon Romanovsky , , Peter Zijlstra , Sebastian Andrzej Siewior , Sebastian Sanchez , Steven Rostedt , "Thomas Gleixner" Subject: Re: [PATCH 1/2] IB/hfi1: Use preempt_{dis,en}able_nort() Message-ID: <20171005141744.GC21185@jcartwri.amer.corp.natinst.com> References: <20171003154920.31566-1-acme@kernel.org> <20171003154920.31566-2-acme@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20171003154920.31566-2-acme@kernel.org> User-Agent: Mutt/1.9.0 (2017-09-02) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-05_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_policy_notspam policy=outbound_policy score=30 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=30 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710050200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 03, 2017 at 12:49:19PM -0300, Arnaldo Carvalho de Melo wrote: > From: Arnaldo Carvalho de Melo > > sc_buffer_alloc() disables preemption that will be reenabled by either > pio_copy() or seg_pio_copy_end(). But before disabling preemption it > grabs a spin lock that will be dropped after it disables preemption, > which ends up triggering a warning in migrate_disable() later on. > > spin_lock_irqsave(&sc->alloc_lock) > migrate_disable() ++p->migrate_disable -> 2 > preempt_disable() > spin_unlock_irqrestore(&sc->alloc_lock) > migrate_enable() in_atomic(), so just returns, migrate_disable stays at 2 > spin_lock_irqsave(some other lock) -> b00m > > And the WARN_ON code ends up tripping over this over and over in > log_store(). > > Sequence captured via ftrace_dump_on_oops + crash utility 'dmesg' > command. > > [512258.613862] sm-3297 16 .....11 359465349134644: sc_buffer_alloc <-hfi1_verbs_send_pio > [512258.613876] sm-3297 16 .....11 359465349134719: migrate_disable <-sc_buffer_alloc > [512258.613890] sm-3297 16 .....12 359465349134798: rt_spin_lock <-sc_buffer_alloc > [512258.613903] sm-3297 16 ....112 359465349135481: rt_spin_unlock <-sc_buffer_alloc > [512258.613916] sm-3297 16 ....112 359465349135556: migrate_enable <-sc_buffer_alloc > [512258.613935] sm-3297 16 ....112 359465349135788: seg_pio_copy_start <-hfi1_verbs_send_pio > [512258.613954] sm-3297 16 ....112 359465349136273: update_sge <-hfi1_verbs_send_pio > [512258.613981] sm-3297 16 ....112 359465349136373: seg_pio_copy_mid <-hfi1_verbs_send_pio > [512258.613999] sm-3297 16 ....112 359465349136873: update_sge <-hfi1_verbs_send_pio > [512258.614017] sm-3297 16 ....112 359465349136956: seg_pio_copy_mid <-hfi1_verbs_send_pio > [512258.614035] sm-3297 16 ....112 359465349137221: seg_pio_copy_end <-hfi1_verbs_send_pio > [512258.614048] sm-3297 16 .....12 359465349137360: migrate_disable <-hfi1_verbs_send_pio > [512258.614065] sm-3297 16 .....12 359465349137476: warn_slowpath_null <-migrate_disable > [512258.614081] sm-3297 16 .....12 359465349137564: __warn <-warn_slowpath_null > [512258.614088] sm-3297 16 .....12 359465349137958: printk <-__warn > [512258.614096] sm-3297 16 .....12 359465349138055: vprintk_default <-printk > [512258.614104] sm-3297 16 .....12 359465349138144: vprintk_emit <-vprintk_default > [512258.614111] sm-3297 16 d....12 359465349138312: _raw_spin_lock <-vprintk_emit > [512258.614119] sm-3297 16 d...112 359465349138789: log_store <-vprintk_emit > [512258.614127] sm-3297 16 .....12 359465349139068: migrate_disable <-vprintk_emit > > According to a discussion (see Link: below) on the linux-rt-users > mailing list, this locking is done for performance reasons, not for > correctness, so use the _nort() variants to avoid the above problem. > > Suggested-by: Julia Cartwright > Cc: Clark Williams > Cc: Dean Luick > Cc: Dennis Dalessandro > Cc: Doug Ledford > Cc: Kaike Wan > Cc: Leon Romanovsky > Cc: linux-rdma@vger.kernel.org > Cc: Peter Zijlstra > Cc: Sebastian Andrzej Siewior > Cc: Sebastian Sanchez > Cc: Steven Rostedt > Cc: Thomas Gleixner > Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_20170926210045.GO29872-40jcartwri.amer.corp.natinst.com&d=DwIBaQ&c=I_0YwoKy7z5LMTVdyO6YCiE2uzI1jjZZuIPelcSjixA&r=cAXq_8W9Othb2h8ZcWv8Vw&m=zzKtWJ595HB0jyuiFic0ZEkpmmjvGRXJHkGF27oyvCI&s=J4_Al0cbvQ9PCM3VbqzJ6apmpSZI9Xx7eq6Gcfucp24&e= > Signed-off-by: Arnaldo Carvalho de Melo > --- > drivers/infiniband/hw/hfi1/pio.c | 2 +- > drivers/infiniband/hw/hfi1/pio_copy.c | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/infiniband/hw/hfi1/pio.c b/drivers/infiniband/hw/hfi1/pio.c > index 615be68e40b3..3a30bde9a07b 100644 > --- a/drivers/infiniband/hw/hfi1/pio.c > +++ b/drivers/infiniband/hw/hfi1/pio.c > @@ -1421,7 +1421,7 @@ struct pio_buf *sc_buffer_alloc(struct send_context *sc, u32 dw_len, > > /* there is enough room */ > > - preempt_disable(); > + preempt_disable_nort(); > this_cpu_inc(*sc->buffers_allocated); Have you tried this on RT w/ CONFIG_DEBUG_PREEMPT? I believe that the this_cpu_* operations perform a preemption check, which we'd trip. You may also have to change these to the non-preempt checked variants. Julia