On Thu, Jun 24, 2021 at 08:49:17AM +0000, ruansy.fnst@fujitsu.com wrote:

Hi Darrick,

Do you have any comment on this?

Sorry, was on vacation.

Thanks,
Ruan.

quoted

-----Original Message-----
From: Shiyang Ruan <redacted>
Subject: [PATCH v6.1 6/7] fs/xfs: Handle CoW for fsdax write() path

Hi Darrick,

Since other patches looks good, I post this RFC patch singly to hot-fix the
problem in xfs_dax_write_iomap_ops->iomap_end() of v6 that the error code
was ingored. I will split this in two patches(changes in iomap and xfs
respectively) in next formal version if it looks ok.

====

Introduce a new interface called "iomap_post_actor()" in iomap_ops.  And call
it between ->actor() and ->iomap_end().  It is mean to handle the error code
returned from ->actor().  In this patchset, it is used to remap or cancel the
CoW extents according to the error code.

Signed-off-by: Shiyang Ruan <redacted>
---
 fs/dax.c               | 27 ++++++++++++++++++---------
 fs/iomap/apply.c       |  4 ++++
 fs/xfs/xfs_bmap_util.c |  3 +--
 fs/xfs/xfs_file.c      |  5 +++--
 fs/xfs/xfs_iomap.c     | 33 ++++++++++++++++++++++++++++++++-
 fs/xfs/xfs_iomap.h     | 24 ++++++++++++++++++++++++
 fs/xfs/xfs_iops.c      |  7 +++----
 fs/xfs/xfs_reflink.c   |  3 +--
 include/linux/iomap.h  |  8 ++++++++
 9 files changed, 94 insertions(+), 20 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 93f16210847b..0740c2610b6f 100644
--- a/fs/dax.c
+++ b/fs/dax.c

@@ -1537,7 +1537,7 @@ static vm_fault_t dax_iomap_pte_fault(struct

vm_fault *vmf, pfn_t *pfnp,
 	struct iomap iomap = { .type = IOMAP_HOLE };
 	struct iomap srcmap = { .type = IOMAP_HOLE };
 	unsigned flags = IOMAP_FAULT;
-	int error;
+	int error, copied = PAGE_SIZE;
 	bool write = vmf->flags & FAULT_FLAG_WRITE;
 	vm_fault_t ret = 0, major = 0;
 	void *entry;

@@ -1598,7 +1598,7 @@ static vm_fault_t dax_iomap_pte_fault(struct

vm_fault *vmf, pfn_t *pfnp,
 	ret = dax_fault_actor(vmf, pfnp, &xas, &entry, false, flags,
 			      &iomap, &srcmap);
 	if (ret == VM_FAULT_SIGBUS)
-		goto finish_iomap;
+		goto finish_iomap_actor;

 	/* read/write MAPPED, CoW UNWRITTEN */
 	if (iomap.flags & IOMAP_F_NEW) {

@@ -1607,10 +1607,16 @@ static vm_fault_t dax_iomap_pte_fault(struct

vm_fault *vmf, pfn_t *pfnp,
 		major = VM_FAULT_MAJOR;
 	}

+ finish_iomap_actor:
+	if (ops->iomap_post_actor) {
+		if (ret & VM_FAULT_ERROR)
+			copied = 0;
+		ops->iomap_post_actor(inode, pos, PMD_SIZE, copied, flags,
+				      &iomap, &srcmap);
+	}
+
 finish_iomap:
 	if (ops->iomap_end) {
-		int copied = PAGE_SIZE;
-
 		if (ret & VM_FAULT_ERROR)
 			copied = 0;
 		/*

@@ -1677,7 +1683,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct

vm_fault *vmf, pfn_t *pfnp,
 	pgoff_t max_pgoff;
 	void *entry;
 	loff_t pos;
-	int error;
+	int error, copied = PMD_SIZE;

 	/*
 	 * Check whether offset isn't beyond end of file now. Caller is @@ -1736,12
+1742,15 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf,
pfn_t *pfnp,
 	ret = dax_fault_actor(vmf, pfnp, &xas, &entry, true, flags,
 			      &iomap, &srcmap);

+	if (ret == VM_FAULT_FALLBACK)
+		copied = 0;
+	if (ops->iomap_post_actor) {
+		ops->iomap_post_actor(inode, pos, PMD_SIZE, copied, flags,
+				      &iomap, &srcmap);
+	}
+
 finish_iomap:
 	if (ops->iomap_end) {
-		int copied = PMD_SIZE;
-
-		if (ret == VM_FAULT_FALLBACK)
-			copied = 0;
 		/*
 		 * The fault is done by now and there's no way back (other
 		 * thread may be already happily using PMD we have installed).

diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c index

0493da5286ad..26a54ded184f 100644

--- a/fs/iomap/apply.c
+++ b/fs/iomap/apply.c

@@ -84,6 +84,10 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length,

unsigned flags,
 	written = actor(inode, pos, length, data, &iomap,
 			srcmap.type != IOMAP_HOLE ? &srcmap : &iomap);

+	if (ops->iomap_post_actor) {
+		written = ops->iomap_post_actor(inode, pos, length, written,
+						flags, &iomap, &srcmap);

How many operations actually need an iomap_post_actor?  It's just the
dax ones, right?  Which is ... iomap_truncate_page, iomap_zero_range,
dax_iomap_fault, and dax_iomap_rw, right?  We don't need a post_actor
for other iomap functionality (like FIEMAP, SEEK_DATA/SEEK_HOLE, etc.)
so adding a new function pointer for all operations feels a bit
overbroad.

I had imagined that you'd create a struct dax_iomap_ops to wrap all the
extra functionality that you need for dax operations:

struct dax_iomap_ops {
	struct iomap_ops	iomap_ops;

	int			(*end_io)(inode, pos, length...);
};

And alter the four functions that you need to take the special
dax_iomap_ops.  I guess the downside is that this makes
iomap_truncate_page and iomap_zero_range more complicated, but maybe
it's just time to split those into DAX-specific versions.  Then we'd be
rid of the cross-links betwee fs/iomap/buffered-io.c and fs/dax.c.

quoted

+	}
 out:
 	/*
 	 * Now the data has been copied, commit the range we've copied.  This

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c index

a5e9d7d34023..2a36dc93ff27 100644

--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c

@@ -965,8 +965,7 @@ xfs_free_file_space(
 		return 0;
 	if (offset + len > XFS_ISIZE(ip))
 		len = XFS_ISIZE(ip) - offset;
-	error = iomap_zero_range(VFS_I(ip), offset, len, NULL,
-			&xfs_buffered_write_iomap_ops);
+	error = xfs_iomap_zero_range(ip, offset, len, NULL);
 	if (error)
 		return error;

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 396ef36dcd0a..89406ec6741b

100644

--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c

@@ -684,11 +684,12 @@ xfs_file_dax_write(
 	pos = iocb->ki_pos;

 	trace_xfs_file_dax_write(iocb, from);
-	ret = dax_iomap_rw(iocb, from, &xfs_direct_write_iomap_ops);
+	ret = dax_iomap_rw(iocb, from, &xfs_dax_write_iomap_ops);
 	if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
 		i_size_write(inode, iocb->ki_pos);
 		error = xfs_setfilesize(ip, pos, ret);
 	}
+
 out:
 	if (iolock)
 		xfs_iunlock(ip, iolock);

@@ -1309,7 +1310,7 @@ __xfs_filemap_fault(

 		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL,
 				(write_fault && !vmf->cow_page) ?
-				 &xfs_direct_write_iomap_ops :
+				 &xfs_dax_write_iomap_ops :
 				 &xfs_read_iomap_ops);
 		if (ret & VM_FAULT_NEEDDSYNC)
 			ret = dax_finish_sync_fault(vmf, pe_size, pfn); diff --git

a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index d154f42e2dc6..2f322e2f8544
100644

--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c

@@ -761,7 +761,8 @@ xfs_direct_write_iomap_begin(

 		/* may drop and re-acquire the ilock */
 		error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
-				&lockmode, flags & IOMAP_DIRECT);
+				&lockmode,
+				(flags & IOMAP_DIRECT) || IS_DAX(inode));
 		if (error)
 			goto out_unlock;
 		if (shared)

@@ -854,6 +855,36 @@ const struct iomap_ops xfs_direct_write_iomap_ops =

{
 	.iomap_begin		= xfs_direct_write_iomap_begin,
 };

+static int
+xfs_dax_write_iomap_post_actor(
+	struct inode		*inode,
+	loff_t			pos,
+	loff_t			length,
+	ssize_t			written,
+	unsigned int		flags,
+	struct iomap		*iomap,
+	struct iomap		*srcmap)
+{
+	int			error = 0;
+	struct xfs_inode	*ip = XFS_I(inode);
+	bool			cow = xfs_is_cow_inode(ip);
+
+	if (written <= 0) {
+		if (cow)
+			xfs_reflink_cancel_cow_range(ip, pos, length, true);
+		return written;
+	}
+
+	if (cow)
+		error = xfs_reflink_end_cow(ip, pos, written);
+	return error ?: written;
+}

This is pretty much the same as what xfs_dio_write_end_io does, right?

I had imagined that you'd change the function signatures to drop the
iocb so that you could reuse this code instead of creating a whole new
callback.

Ah well.  Can I send you some prep patches to clean up some of the weird
iomap code as a preparation series for this?

--D

quoted

+
+const struct iomap_ops xfs_dax_write_iomap_ops = {
+	.iomap_begin		= xfs_direct_write_iomap_begin,
+	.iomap_post_actor	= xfs_dax_write_iomap_post_actor,
+};
+
 static int
 xfs_buffered_write_iomap_begin(
 	struct inode		*inode,

diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h index

7d3703556d0e..fbacf638ab21 100644

--- a/fs/xfs/xfs_iomap.h
+++ b/fs/xfs/xfs_iomap.h

@@ -42,8 +42,32 @@ xfs_aligned_fsb_count(

 extern const struct iomap_ops xfs_buffered_write_iomap_ops;  extern const

struct iomap_ops xfs_direct_write_iomap_ops;
+extern const struct iomap_ops xfs_dax_write_iomap_ops;
 extern const struct iomap_ops xfs_read_iomap_ops;  extern const struct
iomap_ops xfs_seek_iomap_ops;  extern const struct iomap_ops
xfs_xattr_iomap_ops;

+static inline int
+xfs_iomap_zero_range(
+	struct xfs_inode	*ip,
+	loff_t			offset,
+	loff_t			len,
+	bool			*did_zero)
+{
+	return iomap_zero_range(VFS_I(ip), offset, len, did_zero,
+			IS_DAX(VFS_I(ip)) ? &xfs_dax_write_iomap_ops
+					  : &xfs_buffered_write_iomap_ops); }
+
+static inline int
+xfs_iomap_truncate_page(
+	struct xfs_inode	*ip,
+	loff_t			pos,
+	bool			*did_zero)
+{
+	return iomap_truncate_page(VFS_I(ip), pos, did_zero,
+			IS_DAX(VFS_I(ip)) ? &xfs_dax_write_iomap_ops
+					  : &xfs_buffered_write_iomap_ops); }
+
 #endif /* __XFS_IOMAP_H__*/

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index

dfe24b7f26e5..6d936c3e1a6e 100644

--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c

@@ -911,8 +911,8 @@ xfs_setattr_size(
 	 */
 	if (newsize > oldsize) {
 		trace_xfs_zero_eof(ip, oldsize, newsize - oldsize);
-		error = iomap_zero_range(inode, oldsize, newsize - oldsize,
-				&did_zeroing, &xfs_buffered_write_iomap_ops);
+		error = xfs_iomap_zero_range(ip, oldsize, newsize - oldsize,
+				&did_zeroing);
 	} else {
 		/*
 		 * iomap won't detect a dirty page over an unwritten block (or a @@
-924,8 +924,7 @@ xfs_setattr_size(
 						     newsize);
 		if (error)
 			return error;
-		error = iomap_truncate_page(inode, newsize, &did_zeroing,
-				&xfs_buffered_write_iomap_ops);
+		error = xfs_iomap_truncate_page(ip, newsize, &did_zeroing);
 	}

 	if (error)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index

d25434f93235..9a780948dbd0 100644

--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c

@@ -1266,8 +1266,7 @@ xfs_reflink_zero_posteof(
 		return 0;

 	trace_xfs_zero_eof(ip, isize, pos - isize);
-	return iomap_zero_range(VFS_I(ip), isize, pos - isize, NULL,
-			&xfs_buffered_write_iomap_ops);
+	return xfs_iomap_zero_range(ip, isize, pos - isize, NULL);
 }

 /*

diff --git a/include/linux/iomap.h b/include/linux/iomap.h index

95562f863ad0..58f2e1c78018 100644

--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h

@@ -135,6 +135,14 @@ struct iomap_ops {
 			unsigned flags, struct iomap *iomap,
 			struct iomap *srcmap);

+	/*
+	 * Handle the error code from actor(). Do the finishing jobs for extra
+	 * operations, such as CoW, according to whether written is negative.
+	 */
+	int (*iomap_post_actor)(struct inode *inode, loff_t pos, loff_t length,
+			ssize_t written, unsigned flags, struct iomap *iomap,
+			struct iomap *srcmap);
+
 	/*
 	 * Commit and/or unreserve space previous allocated using iomap_begin.
 	 * Written indicates the length of the successful write operation which
--

2.31.1