[PATCH] xfs: introduce "metasync" api to sync metadata to fsblock
Pingfan Liu
kernelfans at gmail.com
Mon Oct 14 19:33:15 AEDT 2019
On Sun, Oct 13, 2019 at 09:34:17AM -0700, Darrick J. Wong wrote:
> On Sun, Oct 13, 2019 at 10:37:00PM +0800, Pingfan Liu wrote:
> > When using fadump (fireware assist dump) mode on powerpc, a mismatch
> > between grub xfs driver and kernel xfs driver has been obsevered. Note:
> > fadump boots up in the following sequence: fireware -> grub reads kernel
> > and initramfs -> kernel boots.
> >
> > The process to reproduce this mismatch:
> > - On powerpc, boot kernel with fadump=on and edit /etc/kdump.conf.
> > - Replacing "path /var/crash" with "path /var/crashnew", then, "kdumpctl
> > restart" to rebuild the initramfs. Detail about the rebuilding looks
> > like: mkdumprd /boot/initramfs-`uname -r`.img.tmp;
> > mv /boot/initramfs-`uname -r`.img.tmp /boot/initramfs-`uname -r`.img
> > sync
> > - "echo c >/proc/sysrq-trigger".
> >
> > The result:
> > The dump image will not be saved under /var/crashnew/* as expected, but
> > still saved under /var/crash.
> >
> > The root cause:
> > As Eric pointed out that on xfs, 'sync' ensures the consistency by writing
> > back metadata to xlog, but not necessary to fsblock. This raises issue if
> > grub can not replay the xlog before accessing the xfs files. Since the
> > above dir entry of initramfs should be saved as inline data with xfs_inode,
> > so xfs_fs_sync_fs() does not guarantee it written to fsblock.
> >
> > umount can be used to write metadata fsblock, but the filesystem can not be
> > umounted if still in use.
> >
> > There are two ways to fix this mismatch, either grub or xfs. It may be
> > easier to do this in xfs side by introducing an interface to flush metadata
> > to fsblock explicitly.
> >
> > With this patch, metadata can be written to fsblock by:
> > # update AIL
> > sync
> > # new introduced interface to flush metadata to fsblock
> > mount -o remount,metasync mountpoint
>
> I think this ought to be an ioctl or some sort of generic call since the
> jbd2 filesystems (ext3, ext4, ocfs2) suffer from the same "$BOOTLOADER
> is too dumb to recover logs but still wants to write to the fs"
> checkpointing problem.
Yes, a syscall sounds more reasonable.
>
> (Or maybe we should just put all that stuff in a vfat filesystem, I
> don't know...)
I think it is unavoidable to involve in each fs' implementation. What
about introducing an interface sync_to_fsblock(struct super_block *sb) in
the struct super_operations, then let each fs manage its own case?
>
> --D
>
> > Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
> > Cc: "Darrick J. Wong" <darrick.wong at oracle.com>
> > Cc: Dave Chinner <dchinner at redhat.com>
> > Cc: Eric Sandeen <esandeen at redhat.com>
> > Cc: Hari Bathini <hbathini at linux.ibm.com>
> > Cc: linuxppc-dev at lists.ozlabs.org
> > To: linux-xfs at vger.kernel.org
> > ---
> > fs/xfs/xfs_mount.h | 1 +
> > fs/xfs/xfs_super.c | 15 ++++++++++++++-
> > fs/xfs/xfs_trans.h | 2 ++
> > fs/xfs/xfs_trans_ail.c | 26 +++++++++++++++++++++++++-
> > fs/xfs/xfs_trans_priv.h | 1 +
> > 5 files changed, 43 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> > index fdb60e0..85f32e6 100644
> > --- a/fs/xfs/xfs_mount.h
> > +++ b/fs/xfs/xfs_mount.h
> > @@ -243,6 +243,7 @@ typedef struct xfs_mount {
> > #define XFS_MOUNT_FILESTREAMS (1ULL << 24) /* enable the filestreams
> > allocator */
> > #define XFS_MOUNT_NOATTR2 (1ULL << 25) /* disable use of attr2 format */
> > +#define XFS_MOUNT_METASYNC (1ull << 26) /* write meta to fsblock */
> >
> > #define XFS_MOUNT_DAX (1ULL << 62) /* TEST ONLY! */
> >
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index 8d1df9f..41df810 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -59,7 +59,7 @@ enum {
> > Opt_filestreams, Opt_quota, Opt_noquota, Opt_usrquota, Opt_grpquota,
> > Opt_prjquota, Opt_uquota, Opt_gquota, Opt_pquota,
> > Opt_uqnoenforce, Opt_gqnoenforce, Opt_pqnoenforce, Opt_qnoenforce,
> > - Opt_discard, Opt_nodiscard, Opt_dax, Opt_err,
> > + Opt_discard, Opt_nodiscard, Opt_dax, Opt_metasync, Opt_err
> > };
> >
> > static const match_table_t tokens = {
> > @@ -106,6 +106,7 @@ static const match_table_t tokens = {
> > {Opt_discard, "discard"}, /* Discard unused blocks */
> > {Opt_nodiscard, "nodiscard"}, /* Do not discard unused blocks */
> > {Opt_dax, "dax"}, /* Enable direct access to bdev pages */
> > + {Opt_metasync, "metasync"}, /* one shot to write meta to fsblock */
> > {Opt_err, NULL},
> > };
> >
> > @@ -338,6 +339,9 @@ xfs_parseargs(
> > mp->m_flags |= XFS_MOUNT_DAX;
> > break;
> > #endif
> > + case Opt_metasync:
> > + mp->m_flags |= XFS_MOUNT_METASYNC;
> > + break;
> > default:
> > xfs_warn(mp, "unknown mount option [%s].", p);
> > return -EINVAL;
> > @@ -1259,6 +1263,9 @@ xfs_fs_remount(
> > mp->m_flags |= XFS_MOUNT_SMALL_INUMS;
> > mp->m_maxagi = xfs_set_inode_alloc(mp, sbp->sb_agcount);
> > break;
> > + case Opt_metasync:
> > + mp->m_flags |= XFS_MOUNT_METASYNC;
> > + break;
> > default:
> > /*
> > * Logically we would return an error here to prevent
> > @@ -1286,6 +1293,12 @@ xfs_fs_remount(
> > }
> > }
> >
> > + if (mp->m_flags & XFS_MOUNT_METASYNC) {
> > + xfs_ail_push_sync(mp->m_ail);
> > + /* one shot flag */
> > + mp->m_flags &= ~XFS_MOUNT_METASYNC;
>
> Wait, so the mount flag magically disables itself?
>
> This really sounds like a system call, not the kinds of long term
> behavioral modifications that mount options are for.
>
Yeah, this one-shot behavior is not suitable for mount.
> > + }
> > +
> > /* ro -> rw */
> > if ((mp->m_flags & XFS_MOUNT_RDONLY) && !(*flags & SB_RDONLY)) {
> > if (mp->m_flags & XFS_MOUNT_NORECOVERY) {
> > diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> > index 64d7f17..fcdb902 100644
> > --- a/fs/xfs/xfs_trans.h
> > +++ b/fs/xfs/xfs_trans.h
> > @@ -242,6 +242,8 @@ void xfs_trans_buf_set_type(struct xfs_trans *, struct xfs_buf *,
> > void xfs_trans_buf_copy_type(struct xfs_buf *dst_bp,
> > struct xfs_buf *src_bp);
> >
> > +void xfs_ail_push_sync(struct xfs_ail *ailp);
> > +
> > extern kmem_zone_t *xfs_trans_zone;
> >
> > #endif /* __XFS_TRANS_H__ */
> > diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> > index 6ccfd75..b8d8df1 100644
> > --- a/fs/xfs/xfs_trans_ail.c
> > +++ b/fs/xfs/xfs_trans_ail.c
> > @@ -488,7 +488,11 @@ xfsaild_push(
> > xfs_trans_ail_cursor_done(&cur);
> > spin_unlock(&ailp->ail_lock);
> >
> > - if (xfs_buf_delwri_submit_nowait(&ailp->ail_buf_list))
> > + if (unlikely(mp->m_flags & XFS_MOUNT_METASYNC)) {
> > + xfs_buf_delwri_submit(&ailp->ail_buf_list);
>
> I guess this never fails, because write IO is 100% successful?
No, unfortunately, xfs_buf_delwri_submit() can return error. Do you
suggest to pass the error to the sync call?
Thanks for your kindly review.
Regards,
Pingfan
[Keep the following original content unchanged. And cc Jan Kara, linux-fsdevel due to this
design may touch the vfs layer]
>
> --D
>
> > + ailp->ail_log_flush++;
> > + wake_up_all(&ailp->pushed_que);
> > + } else if (xfs_buf_delwri_submit_nowait(&ailp->ail_buf_list))
> > ailp->ail_log_flush++;
> >
> > if (!count || XFS_LSN_CMP(lsn, target) >= 0) {
> > @@ -641,6 +645,25 @@ xfs_ail_push(
> > wake_up_process(ailp->ail_task);
> > }
> >
> > +void
> > +xfs_ail_push_sync(
> > + struct xfs_ail *ailp)
> > +{
> > + xfs_lsn_t sync_lsn;
> > + DEFINE_WAIT(wait);
> > +
> > + sync_lsn = xfs_ail_max_lsn(ailp);
> > + for (;;) {
> > + xfs_ail_push(ailp, sync_lsn);
> > + prepare_to_wait(&ailp->pushed_que, &wait, TASK_INTERRUPTIBLE);
> > + if (XFS_LSN_CMP(READ_ONCE(ailp->ail_target_prev),
> > + sync_lsn) >= 0)
> > + break;
> > + schedule();
> > + }
> > + finish_wait(&ailp->pushed_que, &wait);
> > +}
> > +
> > /*
> > * Push out all items in the AIL immediately
> > */
> > @@ -834,6 +857,7 @@ xfs_trans_ail_init(
> > spin_lock_init(&ailp->ail_lock);
> > INIT_LIST_HEAD(&ailp->ail_buf_list);
> > init_waitqueue_head(&ailp->ail_empty);
> > + init_waitqueue_head(&ailp->pushed_que);
> >
> > ailp->ail_task = kthread_run(xfsaild, ailp, "xfsaild/%s",
> > ailp->ail_mount->m_fsname);
> > diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
> > index 2e073c1..9fe3cc6 100644
> > --- a/fs/xfs/xfs_trans_priv.h
> > +++ b/fs/xfs/xfs_trans_priv.h
> > @@ -61,6 +61,7 @@ struct xfs_ail {
> > int ail_log_flush;
> > struct list_head ail_buf_list;
> > wait_queue_head_t ail_empty;
> > + wait_queue_head_t pushed_que;
> > };
> >
> > /*
> > --
> > 2.7.5
> >
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