Re: [PATCH v7] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Aug 29, 2022 at 06:02:11PM +0800, Shiyang Ruan wrote:
> 
> 
> 在 2022/8/27 5:35, Dan Williams 写道:
> > Shiyang Ruan wrote:
> > > This patch is inspired by Dan's "mm, dax, pmem: Introduce
> > > dev_pagemap_failure()"[1].  With the help of dax_holder and
> > > ->notify_failure() mechanism, the pmem driver is able to ask filesystem
> > > (or mapped device) on it to unmap all files in use and notify processes
> > > who are using those files.
> > > 
> > > Call trace:
> > > trigger unbind
> > >    -> unbind_store()
> > >     -> ... (skip)
> > >      -> devres_release_all()
> > >       -> kill_dax()
> > >        -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE)
> > >         -> xfs_dax_notify_failure()
> > > 
> > > Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
> > > event.  So do not shutdown filesystem directly if something not
> > > supported, or if failure range includes metadata area.  Make sure all
> > > files and processes are handled correctly.
> > > 
> > > ==
> > > Changes since v6:
> > >     1. Rebase on 6.0-rc2 and Darrick's patch[2].
> > > 
> > > Changes since v5:
> > >     1. Renamed MF_MEM_REMOVE to MF_MEM_PRE_REMOVE
> > >     2. hold s_umount before sync_filesystem()
> > >     3. do sync_filesystem() after SB_BORN check
> > >     4. Rebased on next-20220714
> > > 
> > > [1]:
> > > https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
> > > [2]: https://lore.kernel.org/linux-xfs/Yv5wIa2crHioYeRr@magnolia/
> > > 
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> > > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> > > ---
> > >    drivers/dax/super.c         |  3 ++-
> > >    fs/xfs/xfs_notify_failure.c | 15 +++++++++++++++
> > >    include/linux/mm.h          |  1 +
> > >    3 files changed, 18 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > > index 9b5e2a5eb0ae..cf9a64563fbe 100644
> > > --- a/drivers/dax/super.c
> > > +++ b/drivers/dax/super.c
> > > @@ -323,7 +323,8 @@ void kill_dax(struct dax_device *dax_dev)
> > >    		return;
> > >     	if (dax_dev->holder_data != NULL)
> > > -		dax_holder_notify_failure(dax_dev, 0, U64_MAX, 0);
> > > +		dax_holder_notify_failure(dax_dev, 0, U64_MAX,
> > > +				MF_MEM_PRE_REMOVE);
> > >     	clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
> > >    	synchronize_srcu(&dax_srcu);
> > > diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
> > > index 65d5eb20878e..a9769f17e998 100644
> > > --- a/fs/xfs/xfs_notify_failure.c
> > > +++ b/fs/xfs/xfs_notify_failure.c
> > > @@ -77,6 +77,9 @@ xfs_dax_failure_fn(
> > >     	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
> > >    	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
> > > +		/* Do not shutdown so early when device is to be removed */
> > > +		if (notify->mf_flags & MF_MEM_PRE_REMOVE)
> > > +			return 0;
> > >    		notify->want_shutdown = true;
> > >    		return 0;
> > >    	}
> > > @@ -182,12 +185,22 @@ xfs_dax_notify_failure(
> > >    	struct xfs_mount	*mp = dax_holder(dax_dev);
> > >    	u64			ddev_start;
> > >    	u64			ddev_end;
> > > +	int			error;
> > >     	if (!(mp->m_sb.sb_flags & SB_BORN)) {
> > 
> > How are you testing the SB_BORN interactions? I have a fix for this
> > pending here:
> > 
> > https://lore.kernel.org/nvdimm/166153428094.2758201.7936572520826540019.stgit@dwillia2-xfh.jf.intel.com/
> 
> That was my mistake.  Yes, it should be mp->m_super->s_flags.
> 
> (I remember my testcase did pass in my dev version, but now that seems
> impossible.  I think something was wrong when I did the test.)
> 
> > 
> > >    		xfs_warn(mp, "filesystem is not ready for notify_failure()!");
> > >    		return -EIO;
> > >    	}
> > >    +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> > 
> > It appears this patch is corrupted here. I confirmed that b4 sees the
> > same when trying to apply it.
> 
> Can't this patch be applied?  It is based on 6.0-rc2 + Darrick's patch. It's
> also ok to rebase on 6.0-rc3 + Darrick's patch.
> 
> > 
> > > +		xfs_info(mp, "device is about to be removed!");
> > > +		down_write(&mp->m_super->s_umount);
> > > +		error = sync_filesystem(mp->m_super);
> > 
> > This syncs to make data persistent, but for DAX this also needs to get
> > invalidate all current DAX mappings. I do not see that in these changes.
> 
> I'll add it.

Are you guys going to pick up [1]?

--D

[1] https://lore.kernel.org/linux-xfs/Yv5wIa2crHioYeRr@magnolia/

> 
> --
> Thanks,
> Ruan.
> 
> > 
> > > +		up_write(&mp->m_super->s_umount);
> > > +		if (error)
> > > +			return error;
> > > +	}
> > > +
> > >    	if (mp->m_rtdev_targp && mp->m_rtdev_targp->bt_daxdev == dax_dev) {
> > >    		xfs_warn(mp,
> > >    			 "notify_failure() not supported on realtime device!");
> > > @@ -196,6 +209,8 @@ xfs_dax_notify_failure(
> > >     	if (mp->m_logdev_targp && mp->m_logdev_targp->bt_daxdev == dax_dev &&
> > >    	    mp->m_logdev_targp != mp->m_ddev_targp) {
> > > +		if (mf_flags & MF_MEM_PRE_REMOVE)
> > > +			return 0;
> > >    		xfs_err(mp, "ondisk log corrupt, shutting down fs!");
> > >    		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
> > >    		return -EFSCORRUPTED;
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index 982f2607180b..2c7c132e6512 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -3176,6 +3176,7 @@ enum mf_flags {
> > >    	MF_UNPOISON = 1 << 4,
> > >    	MF_SW_SIMULATED = 1 << 5,
> > >    	MF_NO_RETRY = 1 << 6,
> > > +	MF_MEM_PRE_REMOVE = 1 << 7,
> > >    };
> > >    int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> > >    		      unsigned long count, int mf_flags);
> > > -- 
> > > 2.37.2
> > > 
> > > 
> > 
> >