Re: [PATCH 3/3] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

[Shiyang Ruan]

在 2022/9/15 2:15, Darrick J. Wong 写道:
> On Fri, Sep 02, 2022 at 10:36:01AM +0000, 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()   # was pmem driver ->remove() in v1
> >      -> 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.
> >
> > [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> >
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> > ---
> >   drivers/dax/super.c         |  3 ++-
> >   fs/xfs/xfs_notify_failure.c | 23 +++++++++++++++++++++++
> >   include/linux/mm.h          |  1 +
> >   3 files changed, 26 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 3830f908e215..5e04ba7fa403 100644
> > --- a/fs/xfs/xfs_notify_failure.c
> > +++ b/fs/xfs/xfs_notify_failure.c
> > @@ -22,6 +22,7 @@
> >   
> >   #include <linux/mm.h>
> >   #include <linux/dax.h>
> > +#include <linux/fs.h>
> >   
> >   struct xfs_failure_info {
> >   	xfs_agblock_t		startblock;
> > @@ -77,6 +78,9 @@ xfs_dax_failure_fn(
> >   
> >   	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
> >   	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
> > +		/* The device is about to be removed.  Not a really failure. */
> > +		if (notify->mf_flags & MF_MEM_PRE_REMOVE)
> > +			return 0;
> >   		notify->want_shutdown = true;
> >   		return 0;
> >   	}
> > @@ -182,12 +186,23 @@ xfs_dax_notify_failure(
> >   	struct xfs_mount	*mp = dax_holder(dax_dev);
> >   	u64			ddev_start;
> >   	u64			ddev_end;
> > +	int			error;
> >   
> >   	if (!(mp->m_super->s_flags & SB_BORN)) {
> >   		xfs_warn(mp, "filesystem is not ready for notify_failure()!");
> >   		return -EIO;
> >   	}
> >   
> > +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> > +		xfs_info(mp, "device is about to be removed!");
> > +		down_write(&mp->m_super->s_umount);
> > +		error = sync_filesystem(mp->m_super);
> > +		drop_pagecache_sb(mp->m_super, NULL);
> > +		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_debug(mp,
> >   			 "notify_failure() not supported on realtime device!");
> > @@ -196,6 +211,8 @@ 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;
> > @@ -209,6 +226,12 @@ xfs_dax_notify_failure(
> >   	ddev_start = mp->m_ddev_targp->bt_dax_part_off;
> >   	ddev_end = ddev_start + bdev_nr_bytes(mp->m_ddev_targp->bt_bdev) - 1;
> >   
> > +	/* Notify failure on the whole device */
> > +	if (offset == 0 && len == U64_MAX) {
> > +		offset = ddev_start;
> > +		len = bdev_nr_bytes(mp->m_ddev_targp->bt_bdev);
> > +	}
>
> I wonder, won't the trimming code below take care of this?

The len is U64_MAX, so 'offset + len - 1' will overflow.  That can't be 
handled correctly by the trimming code below.


--
Thanks,
Ruan.

> The rest of the patch looks ok to me.
>
> --D
>
> > +
> >   	/* Ignore the range out of filesystem area */
> >   	if (offset + len - 1 < ddev_start)
> >   		return -ENXIO;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 21f8b27bd9fd..9122a1c57dd2 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3183,6 +3183,7 @@ 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