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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0948C43334 for ; Wed, 29 Jun 2022 21:42:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231189AbiF2Vms (ORCPT ); Wed, 29 Jun 2022 17:42:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48946 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231168AbiF2Vmr (ORCPT ); Wed, 29 Jun 2022 17:42:47 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 598C837A17 for ; Wed, 29 Jun 2022 14:42:46 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id E477FB82779 for ; Wed, 29 Jun 2022 21:42:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 908F6C34114; Wed, 29 Jun 2022 21:42:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656538963; bh=lq6cw4xKGX3UBPUgEn2el/5XQvxudlfTq8Ww4MFc2XE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nHvG0lfNVTARcRLDJVeqxLsh0qrjZaTxxQs1Z6oGVZrSKouywwLeiDtVjw6glW7D6 K9gJNYpwb+AitgjFhJ4D/jW4KLjtUMKU81fm/bCG3/mwHKOsEfaTy+LK1u6chut8XJ 4q2NM4qoVo+WIXLKquwiTosnBickBFt4WgebXjkJJz6AGKBbrb4JLoLHtlGoFjbvh2 FpRi9sXcGZBcX4ErjBuUtrDTuQfnb6M3LNMYpZEGG+qklePnlWA47V95bzpA0z/Bmj N50CfJBtq9Dhb9wHyxH8KiOWp7mWFuRQacUN6klwMptbKMSduqyE/oU5+FrUO5ELEI oyxXjaw3/DrXw== Date: Wed, 29 Jun 2022 14:42:43 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 8/9] xfs: add log item precommit operation Message-ID: References: <20220627004336.217366-1-david@fromorbit.com> <20220627004336.217366-9-david@fromorbit.com> <20220629213437.GX227878@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220629213437.GX227878@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Thu, Jun 30, 2022 at 07:34:37AM +1000, Dave Chinner wrote: > On Wed, Jun 29, 2022 at 02:16:03PM -0700, Darrick J. Wong wrote: > > On Mon, Jun 27, 2022 at 10:43:35AM +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 > > > > Oh? > > Stale comment from the original series a couple of year ago, I > think. aha! > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > > index 82cf0189c0db..0acb31093d9f 100644 > > > --- a/fs/xfs/xfs_trans.c > > > +++ b/fs/xfs/xfs_trans.c > > > @@ -844,6 +844,90 @@ 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). > > > + * > > > + * 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, > > > + const struct list_head *a, > > > + const 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 both items are non-sortable, leave them alone. If only one is > > > + * sortable, move the non-sortable item towards the end of the list. > > > + */ > > > + 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; > > > + > > > + diff = lia->li_ops->iop_sort(lia) - lib->li_ops->iop_sort(lib); > > > > I'm kinda surprised the iop_sort method doesn't take both log item > > pointers, like most sorting-comparator functions? But I'll see, maybe > > you're doing something clever wrt ordering of log items of differing > > types, and hence the ->iop_sort implementations are required to return > > some absolute priority or something. > > Nope, we have to order item locking based on an unchanging > characteristic of the object. log items can come and go, we want to > lock items in consistent ascending order, so it has to be based on > some kind of physical characteristic, like inode number, block > address, etc. > > e.g. If all objects are ordered by the physical location, we naturally > get a lock order that can be applied sanely across differing object > types e.g. AG headers will naturally sort and lock before buffers > in the AG itself. e.g. inode cluster buffers for unlinked list > manipulations will always get locked after the AGI.... So if (say) we were going to add dquots to this scheme, we'd probably want to shift all the iop_sort functions to return (say) the xfs_daddr_t of the associated item? (Practically speaking, I don't know that I'd want to tie things down to the disk address quite this soon, and since it's all incore code anyway I don't think the precise type of the return values matter.) Anyway, I'm satisfied-- Reviewed-by: Darrick J. Wong --D > Cheers, > > Dave. > > --D > > > > > + 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; > > > + > > > + /* > > > + * 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. > > > * > > > @@ -869,6 +953,13 @@ __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 9561f193e7e1..64062e3b788b 100644 > > > --- a/fs/xfs/xfs_trans.h > > > +++ b/fs/xfs/xfs_trans.h > > > @@ -71,10 +71,12 @@ 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 *lip); > > > + int (*iop_precommit)(struct xfs_trans *tp, struct xfs_log_item *lip); > > > void (*iop_committing)(struct xfs_log_item *lip, xfs_csn_t seq); > > > - 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 *); > > > > Why did these get moved? > > reasons lost in the mist of times. Probably because I wanted > the sort->precommit->committing->committed to be listed in the order > they are actually called by a transaciton commit? > > -Dave. > > -- > Dave Chinner > david@fromorbit.com