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=-9.8 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,URIBL_BLOCKED autolearn=unavailable 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 CDB1CC43457 for ; Fri, 9 Oct 2020 16:01:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 81A482227E for ; Fri, 9 Oct 2020 16:01:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="E/Ev9lv6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389296AbgJIQBD (ORCPT ); Fri, 9 Oct 2020 12:01:03 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:34044 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388719AbgJIQBD (ORCPT ); Fri, 9 Oct 2020 12:01:03 -0400 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 099G0TaI003895; Fri, 9 Oct 2020 16:00:49 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=KgNlskhh6PAIeUAodtX0YrYqT7e0xrAx3/b6JvHSuz4=; b=E/Ev9lv6B298leOisEStRAN61sSO8wOr2ORnR8ruuGcM0yT8bAakExgw6hAVnpkD7ED4 yXh/geo//84230eRwMBd6i45xRC9d3RPX4hmA1kWlUDGpvyHTEYwk1EUFyl788RkFh85 UxKgpIWplF0Y8RnbiujBhQBUARvWgu+hZhYErfux/nenemxfxvkrvL5H24rP1OmaJCdO 2fLPDthJVSXWhgKtRayV4vI3USytmxNS5em41KRuf66UKKSVXH9d179KXIPGVABN670Z SdYM+e/G/d5l5vMOKG9ffGcrJwyopXj9S1LA4mrwNJCKVyg2+593PAR8Q9QqH7Cv4VGn 9A== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by aserp2130.oracle.com with ESMTP id 342kvytbvj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Fri, 09 Oct 2020 16:00:48 +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 099G0KoE114711; Fri, 9 Oct 2020 16:00:47 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 3429k19sbx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 09 Oct 2020 16:00:47 +0000 Received: from abhmp0004.oracle.com (abhmp0004.oracle.com [141.146.116.10]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 099G0jk8007943; Fri, 9 Oct 2020 16:00:45 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 09 Oct 2020 09:00:44 -0700 Date: Fri, 9 Oct 2020 09:00:40 -0700 From: "Darrick J. Wong" To: Yafang Shao Cc: david@fromorbit.com, hch@infradead.org, willy@infradead.org, mhocko@kernel.org, akpm@linux-foundation.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 2/2] xfs: avoid transaction reservation recursion Message-ID: <20201009160040.GW6540@magnolia> References: <20201009125127.37435-1-laoar.shao@gmail.com> <20201009125127.37435-3-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201009125127.37435-3-laoar.shao@gmail.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9769 signatures=668681 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 phishscore=0 malwarescore=0 mlxlogscore=999 bulkscore=0 suspectscore=5 adultscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010090120 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9769 signatures=668681 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 clxscore=1015 phishscore=0 spamscore=0 mlxlogscore=999 impostorscore=0 priorityscore=1501 suspectscore=5 bulkscore=0 adultscore=0 lowpriorityscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010090120 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Oct 09, 2020 at 08:51:27PM +0800, Yafang Shao wrote: > PF_FSTRANS which is used to avoid transaction reservation recursion, is > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to > PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce > memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which > means to avoid filesystem reclaim recursion. That change is subtle. > Let's take the exmple of the check of WARN_ON_ONCE(current->flags & > PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to > PF_MEMALLOC_NOFS is not proper. > Below comment is quoted from Dave, > > It wasn't for memory allocation recursion protection in XFS - it was for > > transaction reservation recursion protection by something trying to flush > > data pages while holding a transaction reservation. Doing > > this could deadlock the journal because the existing reservation > > could prevent the nested reservation for being able to reserve space > > in the journal and that is a self-deadlock vector. > > IOWs, this check is not protecting against memory reclaim recursion > > bugs at all (that's the previous check [1]). This check is > > protecting against the filesystem calling writepages directly from a > > context where it can self-deadlock. > > So what we are seeing here is that the PF_FSTRANS -> > > PF_MEMALLOC_NOFS abstraction lost all the actual useful information > > about what type of error this check was protecting against. > > As a result, we should reintroduce PF_FSTRANS. As current->journal_info > isn't used in XFS, we can reuse it to indicate whehter the task is in > fstrans or not, Per Willy. To achieve that, four new helpers are introduce > in this patch, per Dave: > - xfs_trans_context_set() > Used in xfs_trans_alloc() > - xfs_trans_context_clear() > Used in xfs_trans_commit() and xfs_trans_cancel() > - xfs_trans_context_update() > Used in xfs_trans_roll() > - xfs_trans_context_active() > To check whehter current is in fs transcation or not > > [1]. Below check is to avoid memory reclaim recursion. > if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == > PF_MEMALLOC)) > goto redirty; > > Cc: Dave Chinner > Cc: Christoph Hellwig > Cc: Michal Hocko > Cc: Darrick J. Wong > Cc: Matthew Wilcox > Signed-off-by: Yafang Shao Well, now that I've killed off (AFAIK) the last nested transaction in XFS I guess it's time to do this... Reviewed-by: Darrick J. Wong --D > --- > fs/iomap/buffered-io.c | 7 ------- > fs/xfs/xfs_aops.c | 23 +++++++++++++++++++++-- > fs/xfs/xfs_linux.h | 4 ---- > fs/xfs/xfs_trans.c | 19 +++++++++---------- > fs/xfs/xfs_trans.h | 30 ++++++++++++++++++++++++++++++ > 5 files changed, 60 insertions(+), 23 deletions(-) > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index bcfc288dba3f..3dc57a38bf0b 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -1498,13 +1498,6 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data) > PF_MEMALLOC)) > goto redirty; > > - /* > - * Given that we do not allow direct reclaim to call us, we should > - * never be called in a recursive filesystem reclaim context. > - */ > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > - goto redirty; > - > /* > * Is this page beyond the end of the file? > * > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > index b35611882ff9..af7270f5f8a9 100644 > --- a/fs/xfs/xfs_aops.c > +++ b/fs/xfs/xfs_aops.c > @@ -62,7 +62,8 @@ xfs_setfilesize_trans_alloc( > * We hand off the transaction to the completion thread now, so > * clear the flag here. > */ > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + xfs_trans_context_clear(tp); > + > return 0; > } > > @@ -125,7 +126,7 @@ xfs_setfilesize_ioend( > * thus we need to mark ourselves as being in a transaction manually. > * Similarly for freeze protection. > */ > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + xfs_trans_context_set(tp); > __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS); > > /* we abort the update if there was an IO error */ > @@ -564,6 +565,16 @@ xfs_vm_writepage( > { > struct xfs_writepage_ctx wpc = { }; > > + /* > + * Given that we do not allow direct reclaim to call us, we should > + * never be called while in a filesystem transaction. > + */ > + if (xfs_trans_context_active()) { > + redirty_page_for_writepage(wbc, page); > + unlock_page(page); > + return 0; > + } > + > return iomap_writepage(page, wbc, &wpc.ctx, &xfs_writeback_ops); > } > > @@ -575,6 +586,14 @@ xfs_vm_writepages( > struct xfs_writepage_ctx wpc = { }; > > xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED); > + > + /* > + * Given that we do not allow direct reclaim to call us, we should > + * never be called while in a filesystem transaction. > + */ > + if (xfs_trans_context_active()) > + return 0; > + > return iomap_writepages(mapping, wbc, &wpc.ctx, &xfs_writeback_ops); > } > > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h > index ab737fed7b12..8a4f6db77e33 100644 > --- a/fs/xfs/xfs_linux.h > +++ b/fs/xfs/xfs_linux.h > @@ -102,10 +102,6 @@ typedef __u32 xfs_nlink_t; > #define xfs_cowb_secs xfs_params.cowb_timer.val > > #define current_cpu() (raw_smp_processor_id()) > -#define current_set_flags_nested(sp, f) \ > - (*(sp) = current->flags, current->flags |= (f)) > -#define current_restore_flags_nested(sp, f) \ > - (current->flags = ((current->flags & ~(f)) | (*(sp) & (f)))) > > #define NBBY 8 /* number of bits per byte */ > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > index ed72867b1a19..5f3a4ff51b3c 100644 > --- a/fs/xfs/xfs_trans.c > +++ b/fs/xfs/xfs_trans.c > @@ -153,8 +153,6 @@ xfs_trans_reserve( > int error = 0; > bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0; > > - /* Mark this thread as being in a transaction */ > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > > /* > * Attempt to reserve the needed disk blocks by decrementing > @@ -163,10 +161,8 @@ xfs_trans_reserve( > */ > if (blocks > 0) { > error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd); > - if (error != 0) { > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + if (error != 0) > return -ENOSPC; > - } > tp->t_blk_res += blocks; > } > > @@ -241,8 +237,6 @@ xfs_trans_reserve( > tp->t_blk_res = 0; > } > > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > - > return error; > } > > @@ -284,6 +278,8 @@ xfs_trans_alloc( > INIT_LIST_HEAD(&tp->t_dfops); > tp->t_firstblock = NULLFSBLOCK; > > + /* Mark this thread as being in a transaction */ > + xfs_trans_context_set(tp); > error = xfs_trans_reserve(tp, resp, blocks, rtextents); > if (error) { > xfs_trans_cancel(tp); > @@ -878,7 +874,8 @@ __xfs_trans_commit( > > xfs_log_commit_cil(mp, tp, &commit_lsn, regrant); > > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + if (!regrant) > + xfs_trans_context_clear(tp); > xfs_trans_free(tp); > > /* > @@ -910,7 +907,8 @@ __xfs_trans_commit( > xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket); > tp->t_ticket = NULL; > } > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + > + xfs_trans_context_clear(tp); > xfs_trans_free_items(tp, !!error); > xfs_trans_free(tp); > > @@ -971,7 +969,7 @@ xfs_trans_cancel( > } > > /* mark this thread as no longer being in a transaction */ > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); > + xfs_trans_context_clear(tp); > > xfs_trans_free_items(tp, dirty); > xfs_trans_free(tp); > @@ -1013,6 +1011,7 @@ xfs_trans_roll( > if (error) > return error; > > + xfs_trans_context_update(trans, *tpp); > /* > * Reserve space in the log for the next transaction. > * This also pushes items in the "AIL", the list of logged items, > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h > index b752501818d2..f84b563438f6 100644 > --- a/fs/xfs/xfs_trans.h > +++ b/fs/xfs/xfs_trans.h > @@ -243,4 +243,34 @@ void xfs_trans_buf_copy_type(struct xfs_buf *dst_bp, > > extern kmem_zone_t *xfs_trans_zone; > > +static inline void > +xfs_trans_context_set(struct xfs_trans *tp) > +{ > + ASSERT(!current->journal_info); > + current->journal_info = tp; > + tp->t_pflags = memalloc_nofs_save(); > +} > + > +static inline void > +xfs_trans_context_update(struct xfs_trans *old, struct xfs_trans *new) > +{ > + ASSERT(current->journal_info == old); > + current->journal_info = new; > +} > + > +static inline void > +xfs_trans_context_clear(struct xfs_trans *tp) > +{ > + ASSERT(current->journal_info == tp); > + current->journal_info = NULL; > + memalloc_nofs_restore(tp->t_pflags); > +} > + > +static inline bool > +xfs_trans_context_active(void) > +{ > + /* Use journal_info to indicate current is in a transaction */ > + return current->journal_info != NULL; > +} > + > #endif /* __XFS_TRANS_H__ */ > -- > 2.17.1 >