From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B78FC4363D for ; Wed, 7 Oct 2020 21:55:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02A7021D6C for ; Wed, 7 Oct 2020 21:55:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="h4gL80CJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728707AbgJGVzw (ORCPT ); Wed, 7 Oct 2020 17:55:52 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:35002 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728649AbgJGVzw (ORCPT ); Wed, 7 Oct 2020 17:55:52 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 097Lnw3M150469; Wed, 7 Oct 2020 21:55:48 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2020-01-29; bh=H7k6BNwzXjF0u4BfECT97BW04dqnjOL2hfZ/+Mv9zWg=; b=h4gL80CJLzSmrV3AOO51ck0U4oqQKZRGtFeAm2KLP4nK8mgPghMvdlzVTzy+nA7yyhhW qn6Hw52pNYg8k8U5gibK/mKvqaqJC1mkMYSiZ2NlzdbeU5UiyW+qqqRmWou288GqZihw I3AeAe1J4YQw6KuZGpT5FbJ1fgQ2PbkMqdPJRJqHpp9FKZ4ErtUhoSyHZIXeMbwr9Pff DQ+WzzjGZ6G/B8yPUxkvW73k9TcR2l4AMmPwQWUndASP+WbS6/rfxFu2qhp/YRV/32VE dMSgS1XwdCmJIqvdjEfwNHVmLbTjozVrPakmYy4WtwIh6X5DydZ6fCbL3Cs0i7IAqyJl tQ== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2120.oracle.com with ESMTP id 33xhxn4gqw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 07 Oct 2020 21:55:48 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 097LoCPp132119; Wed, 7 Oct 2020 21:55:48 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 33y38049jt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 07 Oct 2020 21:55:48 +0000 Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 097LtkFG003099; Wed, 7 Oct 2020 21:55:47 GMT Received: from localhost (/10.159.134.247) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 07 Oct 2020 14:55:46 -0700 Date: Wed, 7 Oct 2020 14:55:45 -0700 From: "Darrick J. Wong" To: Pavel Reichl Cc: Eric Sandeen , linux-xfs@vger.kernel.org Subject: Re: [PATCH v9 4/4] xfs: replace mrlock_t with rw_semaphores Message-ID: <20201007215545.GA6540@magnolia> References: <20201006191541.115364-1-preichl@redhat.com> <20201006191541.115364-5-preichl@redhat.com> <20201007012159.GA49547@magnolia> <066ebfa6-25a2-aee4-a01c-3803ef716361@sandeen.net> <20201007152554.GL49559@magnolia> <4cd57497-4670-f96f-01a0-0c587e77548d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4cd57497-4670-f96f-01a0-0c587e77548d@redhat.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9767 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 malwarescore=0 suspectscore=1 adultscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2010070139 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9767 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 malwarescore=0 bulkscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=1 phishscore=0 mlxlogscore=999 adultscore=0 clxscore=1015 spamscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2010070139 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Oct 07, 2020 at 11:15:32PM +0200, Pavel Reichl wrote: > > > On 10/7/20 5:25 PM, Darrick J. Wong wrote: > > On Wed, Oct 07, 2020 at 09:17:13AM -0500, Eric Sandeen wrote: > >> On 10/6/20 8:21 PM, Darrick J. Wong wrote: > >>> On Tue, Oct 06, 2020 at 09:15:41PM +0200, Pavel Reichl wrote: > >>>> Remove mrlock_t as it does not provide any extra value over > >>>> rw_semaphores. Make i_lock and i_mmaplock native rw_semaphores and > >>>> replace mr*() functions with native rwsem calls. > >>>> > >>>> Release the lock in xfs_btree_split() just before the work-queue > >>>> executing xfs_btree_split_worker() is scheduled and make > >>>> xfs_btree_split_worker() to acquire the lock as a first thing and > >>>> release it just before returning from the function. This it done so the > >>>> ownership of the lock is transfered between kernel threads and thus > >>>> lockdep won't complain about lock being held by a different kernel > >>>> thread. > >>>> > >>>> Signed-off-by: Pavel Reichl > >>>> --- > >>>> fs/xfs/libxfs/xfs_btree.c | 14 +++++++ > >>>> fs/xfs/mrlock.h | 78 --------------------------------------- > >>>> fs/xfs/xfs_inode.c | 36 ++++++++++-------- > >>>> fs/xfs/xfs_inode.h | 4 +- > >>>> fs/xfs/xfs_iops.c | 4 +- > >>>> fs/xfs/xfs_linux.h | 2 +- > >>>> fs/xfs/xfs_super.c | 6 +-- > >>>> 7 files changed, 41 insertions(+), 103 deletions(-) > >>>> delete mode 100644 fs/xfs/mrlock.h > >>>> > >>>> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > >>>> index 2d25bab68764..1d1bb8423688 100644 > >>>> --- a/fs/xfs/libxfs/xfs_btree.c > >>>> +++ b/fs/xfs/libxfs/xfs_btree.c > >>>> @@ -2816,6 +2816,7 @@ xfs_btree_split_worker( > >>>> unsigned long pflags; > >>>> unsigned long new_pflags = PF_MEMALLOC_NOFS; > >>>> > >>>> + rwsem_acquire(&args->cur->bc_ino.ip->i_lock.dep_map, 0, 0, _RET_IP_); > >>> These calls also need a comment explaining just what they're doing. > >>> > >>>> /* > >>>> * we are in a transaction context here, but may also be doing work > >>>> * in kswapd context, and hence we may need to inherit that state > >>>> @@ -2832,6 +2833,7 @@ xfs_btree_split_worker( > >>>> complete(args->done); > >>>> > >>>> current_restore_flags_nested(&pflags, new_pflags); > >>>> + rwsem_release(&args->cur->bc_ino.ip->i_lock.dep_map, _THIS_IP_); > >>> Note that as soon as you call complete(), xfs_btree_split can wake up > >>> and return, which means that *args could now point to reclaimed stack > >>> space. This leads to crashes and memory corruption in generic/562 on > >>> a 1k block filesystem (though in principle this can happen anywhere): > >> > >> > >> What's the right way out of this; store *ip when we enter the function > >> and use that to get to the map, rather than args i guess? > > > > Er, no, because the worker could also get preempted right after > > complete() and take so long to get rescheduled that the the inode have > > been reclaimed. Think about it -- the original thread is waiting on the > > completion that it passed to the worker through $args, and therefore the > > worker cannot touch any of the resources it was accessing through $args > > after calling complete().... > > Hi, > > thanks for the comments, however for some reason I cannot reproduce > the same memory corruption you are getting. Do you have full preempt enabled? > Do you think that moving the 'rwsem_release()' right before the > 'complete()' should fix the problem? > > Something like: > > > + /* > + * Update lockdep's lock ownership information to point to > + * this thread as the thread that scheduled this worker is waiting > + * for it's completion. Nit: "it's" is always a contraction of "it is"; "its" is correct (posessive) form here. Otherwise, this looks fine to me. --D > + */ > rwsem_acquire(&args->cur->bc_ino.ip->i_lock.dep_map, 0, 0, _RET_IP_); > /* > * we are in a transaction context here, but may also be doing work > @@ -2830,10 +2835,15 @@ xfs_btree_split_worker( > > args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, > args->key, args->curp, args->stat); > + /* > + * Update lockdep's lock ownership information to reflect that we will > + * be transferring the ilock from this worker back to the scheduling > + * thread. > + */ > + rwsem_release(&args->cur->bc_ino.ip->i_lock.dep_map, _THIS_IP_); > complete(args->done); > > current_restore_flags_nested(&pflags, new_pflags); > - rwsem_release(&args->cur->bc_ino.ip->i_lock.dep_map, _THIS_IP_); > > > > > > > --D > > > >> Thanks, > >> -Eric > > >