Re: [PATCH v11 2/2] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

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

On Thu, Apr 06, 2023 at 06:50:22PM +0800, Shiyang Ruan wrote:
> 
> 
> 在 2023/4/5 1:45, Darrick J. Wong 写道:
> > On Tue, Mar 28, 2023 at 09:41:46AM +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()
> > >      -> kill_dax()
> > >       -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE)
> > >        -> xfs_dax_notify_failure()
> > >        `-> freeze_super()
> > >        `-> do xfs rmap
> > >        ` -> mf_dax_kill_procs()
> > >        `  -> collect_procs_fsdax()    // all associated
> > >        `  -> unmap_and_kill()
> > >        ` -> invalidate_inode_pages2() // drop file's cache
> > >        `-> thaw_super()
> > > 
> > > Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
> > > event.  Freeze the filesystem to prevent new dax mapping being created.
> > > And 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.  Also drop the cache of associated
> > > files before pmem is removed.
> > > 
> > > [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
> > > 
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> > > ---
> > >   drivers/dax/super.c         |  3 +-
> > >   fs/xfs/xfs_notify_failure.c | 56 +++++++++++++++++++++++++++++++++----
> > >   include/linux/mm.h          |  1 +
> > >   mm/memory-failure.c         | 17 ++++++++---
> > >   4 files changed, 67 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > > index c4c4728a36e4..2e1a35e82fce 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 1e2eddb8f90f..1b4eff43f9b5 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;
> > > @@ -73,10 +74,16 @@ xfs_dax_failure_fn(
> > >   	struct xfs_mount		*mp = cur->bc_mp;
> > >   	struct xfs_inode		*ip;
> > >   	struct xfs_failure_info		*notify = data;
> > > +	struct address_space		*mapping;
> > > +	pgoff_t				pgoff;
> > > +	unsigned long			pgcnt;
> > >   	int				error = 0;
> > >   	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;
> > >   	}
> > > @@ -92,10 +99,18 @@ xfs_dax_failure_fn(
> > >   		return 0;
> > >   	}
> > > -	error = mf_dax_kill_procs(VFS_I(ip)->i_mapping,
> > > -				  xfs_failure_pgoff(mp, rec, notify),
> > > -				  xfs_failure_pgcnt(mp, rec, notify),
> > > -				  notify->mf_flags);
> > > +	mapping = VFS_I(ip)->i_mapping;
> > > +	pgoff = xfs_failure_pgoff(mp, rec, notify);
> > > +	pgcnt = xfs_failure_pgcnt(mp, rec, notify);
> > > +
> > > +	/* Continue the rmap query if the inode isn't a dax file. */
> > > +	if (dax_mapping(mapping))
> > > +		error = mf_dax_kill_procs(mapping, pgoff, pgcnt,
> > > +				notify->mf_flags);
> > > +
> > > +	/* Invalidate the cache anyway. */
> > > +	invalidate_inode_pages2_range(mapping, pgoff, pgoff + pgcnt - 1);
> > > +
> > >   	xfs_irele(ip);
> > >   	return error;
> > >   }
> > > @@ -164,11 +179,25 @@ xfs_dax_notify_ddev_failure(
> > >   	}
> > >   	xfs_trans_cancel(tp);
> > > +
> > > +	/* Unfreeze filesystem anyway if it is freezed before. */
> > > +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> > > +		error = thaw_super(mp->m_super);
> > > +		if (error)
> > > +			return error;
> > 
> > If someone *else* wanders in and thaws the fs, you'll get EINVAL here.
> > 
> > I guess that's useful for knowing if someone's screwed up the freeze
> > state on us, but ... really, don't you want to make sure you've gotten
> > the freeze and nobody else can take it away?
> 
> Ok, I know it now.
> > 
> > I think you want the kernel-initiated freeze proposed by Luis here:
> > https://lore.kernel.org/linux-fsdevel/20230114003409.1168311-4-mcgrof@kernel.org/
> 
> This patch gives userspace higher priority to do freeze/thaw then
> kernelspace.  Userspace can thaw it even when kernelspace needs the freeze
> state.  But I think it can't happen in this case.  Kernelspace(in this case)
> should hold the freeze state and, IOW, has higher priority than userspace.
> I think we could change the @usercall to @priority.
> 
> -int freeze_super(struct super_block *sb)
> +int freeze_super(struct super_block *sb, int priority)
> 
> And priority definitions like:
> #define FREEZE_PRO_AUTO           0  // for auto freeze

What is an auto-freeze, and who would be calling it?  I suspect we
could get by with "exclusive" and "non-exclusive".  Non-exclusive is the
free-for-all we have now where any userspace can thaw, and exclusive is
for kernel users (like PRE_REMOVE) who want to block everyone else from
thawing.

> #define FREEZE_PRO_USERCALL       1  // for user call
> #define FREEZE_PRO_KERNELCALL     2  // for kernel call

"Linux 6.5, now with FREEZE PRO!!!!" ;)

THAW_PROT_* since we're really protecting who gets to thaw the fs; and
"PROT" is a more customary mnemonic for 'protection.

--D

> 
> 
> --
> Thanks,
> Ruan.
> 
> > 
> > Also: Is Fujitsu still pursuing pmem products?  Even though Optane is
> > dead?  I'm no longer sure of what the roadmap is for all this fsdax code
> > and whatnot.
> > 
> > --D
> > 
> > > +	}
> > > +
> > > +	/*
> > > +	 * Determine how to shutdown the filesystem according to the
> > > +	 * error code and flags.
> > > +	 */
> > >   	if (error || notify.want_shutdown) {
> > >   		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
> > >   		if (!error)
> > >   			error = -EFSCORRUPTED;
> > > -	}
> > > +	} else if (mf_flags & MF_MEM_PRE_REMOVE)
> > > +		xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);
> > > +
> > >   	return error;
> > >   }
> > > @@ -182,6 +211,7 @@ 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()!");
> > > @@ -196,6 +226,8 @@ 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 +241,12 @@ 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);
> > > +	}
> > > +
> > >   	/* Ignore the range out of filesystem area */
> > >   	if (offset + len - 1 < ddev_start)
> > >   		return -ENXIO;
> > > @@ -225,6 +263,14 @@ xfs_dax_notify_failure(
> > >   	if (offset + len - 1 > ddev_end)
> > >   		len = ddev_end - offset + 1;
> > > +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> > > +		xfs_info(mp, "device is about to be removed!");
> > > +		/* Freeze the filesystem to prevent new mappings created. */
> > > +		error = freeze_super(mp->m_super);
> > > +		if (error)
> > > +			return error;
> > > +	}
> > > +
> > >   	return xfs_dax_notify_ddev_failure(mp, BTOBB(offset), BTOBB(len),
> > >   			mf_flags);
> > >   }
> > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > index 1f79667824eb..ac3f22c20e1d 100644
> > > --- a/include/linux/mm.h
> > > +++ b/include/linux/mm.h
> > > @@ -3436,6 +3436,7 @@ 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);
> > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > > index fae9baf3be16..6e6acec45568 100644
> > > --- a/mm/memory-failure.c
> > > +++ b/mm/memory-failure.c
> > > @@ -623,7 +623,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
> > >    */
> > >   static void collect_procs_fsdax(struct page *page,
> > >   		struct address_space *mapping, pgoff_t pgoff,
> > > -		struct list_head *to_kill)
> > > +		struct list_head *to_kill, bool pre_remove)
> > >   {
> > >   	struct vm_area_struct *vma;
> > >   	struct task_struct *tsk;
> > > @@ -631,8 +631,15 @@ static void collect_procs_fsdax(struct page *page,
> > >   	i_mmap_lock_read(mapping);
> > >   	read_lock(&tasklist_lock);
> > >   	for_each_process(tsk) {
> > > -		struct task_struct *t = task_early_kill(tsk, true);
> > > +		struct task_struct *t = tsk;
> > > +		/*
> > > +		 * Search for all tasks while MF_MEM_PRE_REMOVE, because the
> > > +		 * current may not be the one accessing the fsdax page.
> > > +		 * Otherwise, search for the current task.
> > > +		 */
> > > +		if (!pre_remove)
> > > +			t = task_early_kill(tsk, true);
> > >   		if (!t)
> > >   			continue;
> > >   		vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> > > @@ -1732,6 +1739,7 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> > >   	dax_entry_t cookie;
> > >   	struct page *page;
> > >   	size_t end = index + count;
> > > +	bool pre_remove = mf_flags & MF_MEM_PRE_REMOVE;
> > >   	mf_flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> > > @@ -1743,9 +1751,10 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> > >   		if (!page)
> > >   			goto unlock;
> > > -		SetPageHWPoison(page);
> > > +		if (!pre_remove)
> > > +			SetPageHWPoison(page);
> > > -		collect_procs_fsdax(page, mapping, index, &to_kill);
> > > +		collect_procs_fsdax(page, mapping, index, &to_kill, pre_remove);
> > >   		unmap_and_kill(&to_kill, page_to_pfn(page), mapping,
> > >   				index, mf_flags);
> > >   unlock:
> > > -- 
> > > 2.39.2
> > >