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=-7.1 required=3.0 tests=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 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 F3F9BC433E0 for ; Wed, 1 Jul 2020 14:31:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE05D206C3 for ; Wed, 1 Jul 2020 14:31:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VQCz6Nft" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730836AbgGAObH (ORCPT ); Wed, 1 Jul 2020 10:31:07 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53975 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730245AbgGAObH (ORCPT ); Wed, 1 Jul 2020 10:31:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593613864; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=odI6jp+QIuVNBRTQv9UCKfBMg3oow/UWm9p5GmxvyyM=; b=VQCz6Nft1CkliZXUhoP8smX2rzy++9O+jHeBV0yQBoq614G7h3ZCSAccLvKUw3EJcROD5f Xf0FQGsBFTfEUXgnY+eiSHfHphIyrkCiwJ5TR+CnyFqPdNkxcZy8b3KJ2Q74bCvAB4DAno kwFItGrdMQvRtknpasiskmay5KhUMDQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-342-FXgCsFH4PyyFtxmMnUOekA-1; Wed, 01 Jul 2020 10:31:00 -0400 X-MC-Unique: FXgCsFH4PyyFtxmMnUOekA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DC8491B2C99B; Wed, 1 Jul 2020 14:30:59 +0000 (UTC) Received: from bfoster (ovpn-120-48.rdu2.redhat.com [10.10.120.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 621EF4D9E6; Wed, 1 Jul 2020 14:30:59 +0000 (UTC) Date: Wed, 1 Jul 2020 10:30:57 -0400 From: Brian Foster To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 2/4] xfs: add log item precommit operation Message-ID: <20200701143057.GA1087@bfoster> References: <20200623095015.1934171-1-david@fromorbit.com> <20200623095015.1934171-3-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623095015.1934171-3-david@fromorbit.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Jun 23, 2020 at 07:50:13PM +1000, Dave Chinner wrote: > From: Dave Chinner > > For inodes that are dirty, we have an attached cluster buffer that > we want to use to track the dirty inode through the AIL. > Unfortunately, locking the cluster buffer and adding it to the > transaction when the inode is first logged in a transaction leads to > buffer lock ordering inversions. > > The specific problem is ordering against the AGI buffer. When > modifying unlinked lists, the buffer lock order is AGI -> inode > cluster buffer as the AGI buffer lock serialises all access to the > unlinked lists. Unfortunately, functionality like xfs_droplink() > logs the inode before calling xfs_iunlink(), as do various directory > manipulation functions. The inode can be logged way down in the > stack as far as the bmapi routines and hence, without a major > rewrite of lots of APIs there's no way we can avoid the inode being > logged by something until after the AGI has been logged. > > As we are going to be using ordered buffers for inode AIL tracking, > there isn't a need to actually lock that buffer against modification > as all the modifications are captured by logging the inode item > itself. Hence we don't actually need to join the cluster buffer into > the transaction until just before it is committed. This means we do > not perturb any of the existing buffer lock orders in transactions, > and the inode cluster buffer is always locked last in a transaction > that doesn't otherwise touch inode cluster buffers. > > We do this by introducing a precommit log item method. A log item > method is used because it is likely dquots will be moved to this > same ordered buffer tracking scheme and hence will need a similar > callout. This commit just introduces the mechanism; the inode item > implementation is in followup commits. > > The precommit items need to be sorted into consistent order as we > may be locking multiple items here. Hence if we have two dirty > inodes in cluster buffers A and B, and some other transaction has > two separate dirty inodes in the same cluster buffers, locking them > in different orders opens us up to ABBA deadlocks. Hence we sort the > items on the transaction based on the presence of a sort log item > method. > > Signed-off-by: Dave Chinner > --- Seems like a nice abstraction, particularly when you consider the other use cases you described that should fall into place over time. A couple minor comments.. > fs/xfs/xfs_icache.c | 1 + > fs/xfs/xfs_trans.c | 90 +++++++++++++++++++++++++++++++++++++++++++++ > fs/xfs/xfs_trans.h | 6 ++- > 3 files changed, 95 insertions(+), 2 deletions(-) > ... > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > index 3c94e5ff4316..6f350490f84b 100644 > --- a/fs/xfs/xfs_trans.c > +++ b/fs/xfs/xfs_trans.c > @@ -799,6 +799,89 @@ xfs_trans_committed_bulk( > spin_unlock(&ailp->ail_lock); > } > > +/* > + * Sort transaction items prior to running precommit operations. This will > + * attempt to order the items such that they will always be locked in the same > + * order. Items that have no sort function are moved to the end of the list > + * and so are locked last (XXX: need to check the logic matches the comment). > + * Heh, I was going to ask what the expected behavior was with the various !iop_sort() cases and whether we can really expect those items to be isolated at the end of the list. > + * This may need refinement as different types of objects add sort functions. > + * > + * Function is more complex than it needs to be because we are comparing 64 bit > + * values and the function only returns 32 bit values. > + */ > +static int > +xfs_trans_precommit_sort( > + void *unused_arg, > + struct list_head *a, > + struct list_head *b) > +{ > + struct xfs_log_item *lia = container_of(a, > + struct xfs_log_item, li_trans); > + struct xfs_log_item *lib = container_of(b, > + struct xfs_log_item, li_trans); > + int64_t diff; > + > + if (!lia->li_ops->iop_sort && !lib->li_ops->iop_sort) > + return 0; > + if (!lia->li_ops->iop_sort) > + return 1; > + if (!lib->li_ops->iop_sort) > + return -1; I'm a little confused on what these values are supposed to mean if one of the two items is non-sortable. Is the purpose of this simply to move sortable items to the head and non-sortable toward the tail, as noted above? > + > + diff = lia->li_ops->iop_sort(lia) - lib->li_ops->iop_sort(lib); > + if (diff < 0) > + return -1; > + if (diff > 0) > + return 1; > + return 0; > +} > + > +/* > + * Run transaction precommit functions. > + * > + * If there is an error in any of the callouts, then stop immediately and > + * trigger a shutdown to abort the transaction. There is no recovery possible > + * from errors at this point as the transaction is dirty.... > + */ > +static int > +xfs_trans_run_precommits( > + struct xfs_trans *tp) > +{ > + struct xfs_mount *mp = tp->t_mountp; > + struct xfs_log_item *lip, *n; > + int error = 0; > + > + if (XFS_FORCED_SHUTDOWN(mp)) > + return -EIO; > + I'd rather not change behavior here. This effectively overrides the shutdown check in the caller because we get here regardless of whether the transaction has any pre-commit callouts or not. It seems like this is unnecessary, at least for the time being, if the precommit is primarily focused on sorting. Brian > + /* > + * Sort the item list to avoid ABBA deadlocks with other transactions > + * running precommit operations that lock multiple shared items such as > + * inode cluster buffers. > + */ > + list_sort(NULL, &tp->t_items, xfs_trans_precommit_sort); > + > + /* > + * Precommit operations can remove the log item from the transaction > + * if the log item exists purely to delay modifications until they > + * can be ordered against other operations. Hence we have to use > + * list_for_each_entry_safe() here. > + */ > + list_for_each_entry_safe(lip, n, &tp->t_items, li_trans) { > + if (!test_bit(XFS_LI_DIRTY, &lip->li_flags)) > + continue; > + if (lip->li_ops->iop_precommit) { > + error = lip->li_ops->iop_precommit(tp, lip); > + if (error) > + break; > + } > + } > + if (error) > + xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE); > + return error; > +} > + > /* > * Commit the given transaction to the log. > * > @@ -823,6 +906,13 @@ __xfs_trans_commit( > > trace_xfs_trans_commit(tp, _RET_IP_); > > + error = xfs_trans_run_precommits(tp); > + if (error) { > + if (tp->t_flags & XFS_TRANS_PERM_LOG_RES) > + xfs_defer_cancel(tp); > + goto out_unreserve; > + } > + > /* > * Finish deferred items on final commit. Only permanent transactions > * should ever have deferred ops. > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h > index b752501818d2..26ea19bd0621 100644 > --- a/fs/xfs/xfs_trans.h > +++ b/fs/xfs/xfs_trans.h > @@ -70,10 +70,12 @@ struct xfs_item_ops { > void (*iop_format)(struct xfs_log_item *, struct xfs_log_vec *); > void (*iop_pin)(struct xfs_log_item *); > void (*iop_unpin)(struct xfs_log_item *, int remove); > - uint (*iop_push)(struct xfs_log_item *, struct list_head *); > + uint64_t (*iop_sort)(struct xfs_log_item *); > + int (*iop_precommit)(struct xfs_trans *, struct xfs_log_item *); > void (*iop_committing)(struct xfs_log_item *, xfs_lsn_t commit_lsn); > - void (*iop_release)(struct xfs_log_item *); > xfs_lsn_t (*iop_committed)(struct xfs_log_item *, xfs_lsn_t); > + uint (*iop_push)(struct xfs_log_item *, struct list_head *); > + void (*iop_release)(struct xfs_log_item *); > int (*iop_recover)(struct xfs_log_item *lip, struct xfs_trans *tp); > bool (*iop_match)(struct xfs_log_item *item, uint64_t id); > }; > -- > 2.26.2.761.g0e0b3e54be >