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 BAB1CC433F5 for ; Wed, 13 Apr 2022 02:07:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231576AbiDMCJU (ORCPT ); Tue, 12 Apr 2022 22:09:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230436AbiDMCJN (ORCPT ); Tue, 12 Apr 2022 22:09:13 -0400 Received: from mail-pl1-x62b.google.com (mail-pl1-x62b.google.com [IPv6:2607:f8b0:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E3E014F44C for ; Tue, 12 Apr 2022 19:06:51 -0700 (PDT) Received: by mail-pl1-x62b.google.com with SMTP id y6so708958plg.2 for ; Tue, 12 Apr 2022 19:06:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=0MNiYyg47Q/lgq+p2TnJidv+4v97sJVTq+BwgFSq+VQ=; b=Lpgu/kIIY6OTgkq6DK8AGceWu1W0JSwkDntRla5RelvUGWpCef4ixTRLk0CeQg8uh+ FOdDJCUfB9Gum6HLdD0Qv54dDadV8PRLhEpwklqG9/ZxLMK2ggaz8YeybLNI2CmXSQaB CIzPn8mr7GfABn6kfFCNd0FvU1OjjKt+1d1ZWBZNl6HXGN0xetQzhaTyw1kRDVF3a1VT U7mV2jnhRXrgYDedNMRbb0cBKmZb0sx8bXXilHxQQHeS3ikfhZESBiLkrjEasqxrSKKm z94G3RWuGw9aL9Za7IFByAm9JWMkqZauiXIex4BhIZ933SiUEodMsIXWevWOXUYXfT7s OcOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=0MNiYyg47Q/lgq+p2TnJidv+4v97sJVTq+BwgFSq+VQ=; b=gSEONA8wpeA9vVucmwTaZZl80gfuQwM0Y3Xb2zFJTFLneqS/DIqY/JzAXcmfVRQ/+U u3Hcu9d5rnYRSL932NhjaBn5ZWIr+ZVZu5lzDIa386n+RX4ufxm5ln2pztSfHBQpiUrG BE+oR3EU5DM91ejZgQZ17twIJMbCJoANcPV9H4E54eeK39KAF00v5OgIUf0e9tpg20Ht mgvf3ODn15/9BO01ND2GqPbtR/lmZQJiB4TlPy03A4X0S8GsHDmdbrOqfytKtFSzZubX QOUOM0wacPi9K41yJwUwGZ9zbwTYNA0PFBhA1GBtRCKOxIj9LzSWqj2FdtFpFuK8eDfK V+dQ== X-Gm-Message-State: AOAM530pZpmZgiYO8YSntDX4quB1aI+2qGoVJX3oJ7X1F2b7P3BaIK9M ja1S3ebgrlGOgQcPPFJ45TcKSbtWg31PU/swlB8AXQ== X-Google-Smtp-Source: ABdhPJxWw5xA7X5gjbLtdUOG67b6VL4topnpS9iw/C6hutLuDw/UuVcok1a0F93UlSgXX0Iq41Uluo4OCw+GE3qP/QE= X-Received: by 2002:a17:902:eb92:b0:158:4cc9:698e with SMTP id q18-20020a170902eb9200b001584cc9698emr17120666plg.147.1649815611069; Tue, 12 Apr 2022 19:06:51 -0700 (PDT) MIME-Version: 1.0 References: <20220410160904.3758789-1-ruansy.fnst@fujitsu.com> <20220410160904.3758789-7-ruansy.fnst@fujitsu.com> <20220413000423.GK1544202@dread.disaster.area> In-Reply-To: <20220413000423.GK1544202@dread.disaster.area> From: Dan Williams Date: Tue, 12 Apr 2022 19:06:40 -0700 Message-ID: Subject: Re: [PATCH v12 6/7] xfs: Implement ->notify_failure() for XFS To: Dave Chinner Cc: Shiyang Ruan , Linux Kernel Mailing List , linux-xfs , Linux NVDIMM , Linux MM , linux-fsdevel , "Darrick J. Wong" , Christoph Hellwig , Jane Chu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 12, 2022 at 5:04 PM Dave Chinner wrote: > > On Mon, Apr 11, 2022 at 12:09:03AM +0800, Shiyang Ruan wrote: > > Introduce xfs_notify_failure.c to handle failure related works, such as > > implement ->notify_failure(), register/unregister dax holder in xfs, and > > so on. > > > > If the rmap feature of XFS enabled, we can query it to find files and > > metadata which are associated with the corrupt data. For now all we do > > is kill processes with that file mapped into their address spaces, but > > future patches could actually do something about corrupt metadata. > > > > After that, the memory failure needs to notify the processes who are > > using those files. > > > > Signed-off-by: Shiyang Ruan > > --- > > fs/xfs/Makefile | 5 + > > fs/xfs/xfs_buf.c | 7 +- > > fs/xfs/xfs_fsops.c | 3 + > > fs/xfs/xfs_mount.h | 1 + > > fs/xfs/xfs_notify_failure.c | 219 ++++++++++++++++++++++++++++++++++++ > > fs/xfs/xfs_super.h | 1 + > > 6 files changed, 233 insertions(+), 3 deletions(-) > > create mode 100644 fs/xfs/xfs_notify_failure.c > > > > diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile > > index 04611a1068b4..09f5560e29f2 100644 > > --- a/fs/xfs/Makefile > > +++ b/fs/xfs/Makefile > > @@ -128,6 +128,11 @@ xfs-$(CONFIG_SYSCTL) += xfs_sysctl.o > > xfs-$(CONFIG_COMPAT) += xfs_ioctl32.o > > xfs-$(CONFIG_EXPORTFS_BLOCK_OPS) += xfs_pnfs.o > > > > +# notify failure > > +ifeq ($(CONFIG_MEMORY_FAILURE),y) > > +xfs-$(CONFIG_FS_DAX) += xfs_notify_failure.o > > +endif > > + > > # online scrub/repair > > ifeq ($(CONFIG_XFS_ONLINE_SCRUB),y) > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index f9ca08398d32..9064b8dfbc66 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -5,6 +5,7 @@ > > */ > > #include "xfs.h" > > #include > > +#include > > > > #include "xfs_shared.h" > > #include "xfs_format.h" > > @@ -1911,7 +1912,7 @@ xfs_free_buftarg( > > list_lru_destroy(&btp->bt_lru); > > > > blkdev_issue_flush(btp->bt_bdev); > > - fs_put_dax(btp->bt_daxdev, NULL); > > + fs_put_dax(btp->bt_daxdev, btp->bt_mount); > > > > kmem_free(btp); > > } > > @@ -1964,8 +1965,8 @@ xfs_alloc_buftarg( > > btp->bt_mount = mp; > > btp->bt_dev = bdev->bd_dev; > > btp->bt_bdev = bdev; > > - btp->bt_daxdev = fs_dax_get_by_bdev(bdev, &btp->bt_dax_part_off, NULL, > > - NULL); > > + btp->bt_daxdev = fs_dax_get_by_bdev(bdev, &btp->bt_dax_part_off, mp, > > + &xfs_dax_holder_operations); > > I see a problem with this: we are setting up notify callbacks before > we've even read in the superblock during mount. i.e. we don't even > kow yet if we've got an XFS filesystem on this block device. > > Hence if we get a notification immediately after registering this > notification callback.... > > [...] > > > + > > +static int > > +xfs_dax_notify_ddev_failure( > > + struct xfs_mount *mp, > > + xfs_daddr_t daddr, > > + xfs_daddr_t bblen, > > + int mf_flags) > > +{ > > + struct xfs_trans *tp = NULL; > > + struct xfs_btree_cur *cur = NULL; > > + struct xfs_buf *agf_bp = NULL; > > + int error = 0; > > + xfs_fsblock_t fsbno = XFS_DADDR_TO_FSB(mp, daddr); > > + xfs_agnumber_t agno = XFS_FSB_TO_AGNO(mp, fsbno); > > + xfs_fsblock_t end_fsbno = XFS_DADDR_TO_FSB(mp, daddr + bblen); > > + xfs_agnumber_t end_agno = XFS_FSB_TO_AGNO(mp, end_fsbno); > > .... none of this code is going to function correctly because it > is dependent on the superblock having been read, validated and > copied to the in-memory superblock. > > > + error = xfs_trans_alloc_empty(mp, &tp); > > + if (error) > > + return error; > > ... and it's not valid to use transactions (even empty ones) before > log recovery has completed and set the log up correctly. > > > + > > + for (; agno <= end_agno; agno++) { > > + struct xfs_rmap_irec ri_low = { }; > > + struct xfs_rmap_irec ri_high; > > + struct failure_info notify; > > + struct xfs_agf *agf; > > + xfs_agblock_t agend; > > + > > + error = xfs_alloc_read_agf(mp, tp, agno, 0, &agf_bp); > > + if (error) > > + break; > > + > > + cur = xfs_rmapbt_init_cursor(mp, tp, agf_bp, agf_bp->b_pag); > > ... and none of the structures this rmapbt walk is dependent on > (e.g. perag structures) have been initialised yet so there's null > pointer dereferences going to happen here. > > Perhaps even worse is that the rmapbt is not guaranteed to be in > consistent state until after log recovery has completed, so this > walk could get stuck forever in a stale on-disk cycle that > recovery would have corrected.... > > Hence these notifications need to be delayed until after the > filesystem is mounted, all the internal structures have been set up > and log recovery has completed. So I think this gets back to the fact that there will eventually be 2 paths into this notifier. One will be the currently proposed synchronous / CPU-consumes-poison while accessing the filesystem (potentially even while recovery is running), and another will be in response to some asynchronous background scanning. I am thinking that the latter would be driven from a userspace daemon reconciling background scan events and notifying the filesystem and any other interested party. All that to say, I think it is ok / expected for the filesystem to drop notifications on the floor when it is not ready to handle them. For example there are no processes to send SIGBUS to if the filesystem has not even finished mount. It is then up to userspace to replay any relevant error notifications that may be pending after mount completes to sync the filesystem with the current state of the hardware.