Re: [RFC PATCH v11.1 2/2] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

[Jan Kara <jack@suse.cz>]

On Thu 20-04-23 10:07:39, Shiyang Ruan wrote:
> 在 2023/4/12 18:52, Shiyang Ruan 写道:
> > This is a RFC HOTFIX.
> > 
> > This hotfix adds a exclusive forzen state to make sure any others won't
> > thaw the fs during xfs_dax_notify_failure():
> > 
> >    #define SB_FREEZE_EXCLUSIVE	(SB_FREEZE_COMPLETE + 2)
> > Using +2 here is because Darrick's patch[0] is using +1.  So, should we
> > make these definitions global?
> > 
> > Another thing I can't make up my mind is: when another freezer has freeze
> > the fs, should we wait unitl it finish, or print a warning in dmesg and
> > return -EBUSY?
> > 
> > Since there are at least 2 places needs exclusive forzen state, I think
> > we can refactor helper functions of freeze/thaw for them.  e.g.
> >    int freeze_super_exclusive(struct super_block *sb, int frozen);
> >    int thaw_super_exclusive(struct super_block *sb, int frozen);
> > 
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=repair-fscounters&id=c3a0d1de4d54ffb565dbc7092dfe1fb851940669

I'm OK with the idea of new freeze state that does not allow userspace to
thaw the filesystem. But I don't really like the guts of filesystem
freezing being replicated inside XFS. It is bad enough that they are
replicated in [0], replicating them *once more* in another XFS file shows
we are definitely doing something wrong. And Luis will need yet another
incantation of the exlusive freeze for suspend-to-disk. So please guys get
together and reorganize the generic freezing code so that it supports
exclusive freeze (for in-kernel users) and works for your usecases instead
of replicating it inside XFS...

								Honza

> > --- Original commit message ---
> > 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.  Also introduce a exclusive freeze/thaw to lock the filesystem to
> > prevent new dax mapping from 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 | 151 ++++++++++++++++++++++++++++++++++--
> >   include/linux/mm.h          |   1 +
> >   mm/memory-failure.c         |  17 +++-
> >   4 files changed, 162 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..796dd954d33a 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;
> >   	}
> > @@ -92,14 +99,120 @@ 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;
> >   }
> > +#define SB_FREEZE_EXCLUSIVE	(SB_FREEZE_COMPLETE + 2)
> > +
> > +static int
> > +xfs_dax_notify_failure_freeze(
> > +	struct xfs_mount	*mp)
> > +{
> > +	struct super_block	*sb = mp->m_super;
> > +	int			error = 0;
> > +	int			level;
> > +
> > +	/* Wait until we're ready to freeze. */
> > +	down_write(&sb->s_umount);
> > +	while (sb->s_writers.frozen != SB_UNFROZEN) {
> > +		up_write(&sb->s_umount);
> > +
> > +		// just wait, or print warning in dmesg then return -EBUSY?
> > +
> > +		delay(HZ / 10);
> > +		down_write(&sb->s_umount);
> > +	}
> > +
> > +	if (sb_rdonly(sb)) {
> > +		sb->s_writers.frozen = SB_FREEZE_EXCLUSIVE;
> > +		goto out;
> > +	}
> > +
> > +	sb->s_writers.frozen = SB_FREEZE_WRITE;
> > +	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
> > +	up_write(&sb->s_umount);
> > +	percpu_down_write(sb->s_writers.rw_sem + SB_FREEZE_WRITE - 1);
> > +	down_write(&sb->s_umount);
> > +
> > +	/* Now we go and block page faults... */
> > +	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
> > +	percpu_down_write(sb->s_writers.rw_sem + SB_FREEZE_PAGEFAULT - 1);
> > +
> > +	/* All writers are done so after syncing there won't be dirty data */
> > +	error = sync_filesystem(sb);
> > +	if (error) {
> > +		sb->s_writers.frozen = SB_UNFROZEN;
> > +		for (level = SB_FREEZE_PAGEFAULT - 1; level >= 0; level--)
> > +			percpu_up_write(sb->s_writers.rw_sem + level);
> > +		wake_up(&sb->s_writers.wait_unfrozen);
> > +		goto out;
> > +	}
> > +
> > +	/* Now wait for internal filesystem counter */
> > +	sb->s_writers.frozen = SB_FREEZE_FS;
> > +	percpu_down_write(sb->s_writers.rw_sem + SB_FREEZE_FS - 1);
> > +
> > +	/*
> > +	 * To prevent anyone else from unfreezing us, set the VFS freeze level
> > +	 * to one higher than SB_FREEZE_COMPLETE.
> > +	 */
> > +	sb->s_writers.frozen = SB_FREEZE_EXCLUSIVE;
> > +	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
> > +		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0,
> > +				_THIS_IP_);
> > +
> > +out:
> > +	up_write(&sb->s_umount);
> > +	return error;
> > +}
> > +
> > +static void
> > +xfs_dax_notify_failure_thaw(
> > +	struct xfs_mount	*mp)
> > +{
> > +	struct super_block	*sb = mp->m_super;
> > +	int			level;
> > +
> > +	down_write(&sb->s_umount);
> > +	if (sb->s_writers.frozen != SB_FREEZE_EXCLUSIVE) {
> > +		/* somebody snuck in and unfroze us? */
> > +		ASSERT(0);
> > +		up_write(&sb->s_umount);
> > +		return;
> > +	}
> > +
> > +	if (sb_rdonly(sb)) {
> > +		sb->s_writers.frozen = SB_UNFROZEN;
> > +		goto out;
> > +	}
> > +
> > +	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
> > +		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0,
> > +				_THIS_IP_);
> > +
> > +	sb->s_writers.frozen = SB_UNFROZEN;
> > +	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
> > +		percpu_up_write(sb->s_writers.rw_sem + level);
> > +
> > +out:
> > +	wake_up(&sb->s_writers.wait_unfrozen);
> > +	up_write(&sb->s_umount);
> > +}
> > +
> >   static int
> >   xfs_dax_notify_ddev_failure(
> >   	struct xfs_mount	*mp,
> > @@ -164,11 +277,22 @@ xfs_dax_notify_ddev_failure(
> >   	}
> >   	xfs_trans_cancel(tp);
> > +
> > +	/* Thaw the fs if it is freezed before. */
> > +	if (mf_flags & MF_MEM_PRE_REMOVE)
> > +		xfs_dax_notify_failure_thaw(mp);
> > +
> > +	/*
> > +	 * 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 +306,7 @@ 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 +321,8 @@ 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 +336,12 @@ 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 +358,14 @@ 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 fs to prevent new mappings from being created. */
> > +		error = xfs_dax_notify_failure_freeze(mp);
> > +		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:
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR