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 DABC0C43334 for ; Wed, 29 Jun 2022 21:16:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229784AbiF2VQL (ORCPT ); Wed, 29 Jun 2022 17:16:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230015AbiF2VQK (ORCPT ); Wed, 29 Jun 2022 17:16:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01B8B3FD88 for ; Wed, 29 Jun 2022 14:16:05 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 787F160F6E for ; Wed, 29 Jun 2022 21:16:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D49F3C34114; Wed, 29 Jun 2022 21:16:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656537363; bh=4bvO2MLvt5RQhmE+BMkseqM2OqAqv7hxJGixWo+ulW4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=P+RkzWx5NmSZcd9zV24/GTNIQCMsOctA7U/DQ/AMaoAVOSfwPCTvGFLrLDD7ys4d/ CVfxDGHPeebwLttnFuzETj91YADFMeToSeHlhKBEF1kZPb9CPumx+n7eL6hcKvbkEd 0qaL+rQ/Y1fCEtK25bo1TGF0bLyY/wueSrGhBfxNPG9c8FIcyFm8scrG/IXVtWrlm3 CuyCYwnaHq/YqqGMMSsWspx7ok1ktHvTgDToHMmjL0e/6PAIbIsMsMaBkYNQU9Cmvm 5qglxnIBVWLLYdu34HxHux1kxVuiyBNBrAiJjklsyYflgij1o8zL7ZPQaChqm7VWMh cNn9SuQdKzZAQ== Date: Wed, 29 Jun 2022 14:16:03 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220627004336.217366-9-david@fromorbit.com> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org 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? > 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 > --- > fs/xfs/xfs_icache.c | 1 + > fs/xfs/xfs_trans.c | 91 +++++++++++++++++++++++++++++++++++++++++++++ > fs/xfs/xfs_trans.h | 6 ++- > 3 files changed, 96 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index 9fc324a29535..374b3bafaeb0 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -914,6 +914,7 @@ xfs_reclaim_inode( > ip->i_checked = 0; > spin_unlock(&ip->i_flags_lock); > > + ASSERT(!ip->i_itemp || ip->i_itemp->ili_item.li_buf == NULL); > xfs_iunlock(ip, XFS_ILOCK_EXCL); > > XFS_STATS_INC(ip->i_mount, xs_ig_reclaims); > 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. --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? --D > int (*iop_recover)(struct xfs_log_item *lip, > struct list_head *capture_list); > bool (*iop_match)(struct xfs_log_item *item, uint64_t id); > -- > 2.36.1 >