[PATCH v8 05/20] fs/dax: Create a common implementation to break DAX layouts

Alistair Popple
2025-02-18T03:56:22Z

Prior to freeing a block file systems supporting FS DAX must check
that the associated pages are both unmapped from user-space and not
undergoing DMA or other access from eg. get_user_pages(). This is
achieved by unmapping the file range and scanning the FS DAX
page-cache to see if any pages within the mapping have an elevated
refcount.

This is done using two functions - dax_layout_busy_page_range() which
returns a page to wait for the refcount to become idle on. Rather than
open-code this introduce a common implementation to both unmap and
wait for the page to become idle.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>

---

Changes for v7:

- Fix smatch warning, also reported by Dan and Darrick
- Make sure xfs_break_layouts() can return -ERESTARTSYS, reported by
Darrick
- Use common definition of dax_page_is_idle()
- Removed misplaced hunk changing madvise
- Renamed dax_break_mapping() to dax_break_layout() suggested by Dan
- Fix now unused variables in ext4

Changes for v5:

- Don't wait for idle pages on non-DAX mappings

Changes for v4:

- Fixed some build breakage due to missing symbol exports reported by
John Hubbard (thanks!).
---
fs/dax.c | 33 +++++++++++++++++++++++++++++++++
fs/ext4/inode.c | 13 +------------
fs/fuse/dax.c | 27 +++------------------------
fs/xfs/xfs_inode.c | 26 +++++++-------------------
fs/xfs/xfs_inode.h | 2 +-
include/linux/dax.h | 23 ++++++++++++++++++-----
6 files changed, 63 insertions(+), 61 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index f5fdb43..f1945aa 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -846,6 +846,39 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
return ret;
}

+static int wait_page_idle(struct page *page,
+ void (cb)(struct inode *),
+ struct inode *inode)
+{
+ return ___wait_var_event(page, dax_page_is_idle(page),
+ TASK_INTERRUPTIBLE, 0, 0, cb(inode));
+}
+
+/*
+ * Unmaps the inode and waits for any DMA to complete prior to deleting the
+ * DAX mapping entries for the range.
+ */
+int dax_break_layout(struct inode *inode, loff_t start, loff_t end,
+ void (cb)(struct inode *))
+{
+ struct page *page;
+ int error = 0;
+
+ if (!dax_mapping(inode->i_mapping))
+ return 0;
+
+ do {
+ page = dax_layout_busy_page_range(inode->i_mapping, start, end);
+ if (!page)
+ break;
+
+ error = wait_page_idle(page, cb, inode);
+ } while (error == 0);
+
+ return error;
+}
+EXPORT_SYMBOL_GPL(dax_break_layout);
+
/*
* Invalidate DAX entry if it is clean.
*/
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index cc1acb1..2342bac 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3911,21 +3911,10 @@ static void ext4_wait_dax_page(struct inode *inode)

int ext4_break_layouts(struct inode *inode)
{
- struct page *page;
- int error;
-
if (WARN_ON_ONCE(!rwsem_is_locked(&inode->i_mapping->invalidate_lock)))
return -EINVAL;

- do {
- page = dax_layout_busy_page(inode->i_mapping);
- if (!page)
- return 0;
-
- error = dax_wait_page_idle(page, ext4_wait_dax_page, inode);
- } while (error == 0);
-
- return error;
+ return dax_break_layout_inode(inode, ext4_wait_dax_page);
}

/*
diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index bf6faa3..0502bf3 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -666,33 +666,12 @@ static void fuse_wait_dax_page(struct inode *inode)
filemap_invalidate_lock(inode->i_mapping);
}

-/* Should be called with mapping->invalidate_lock held exclusively */
-static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
- loff_t start, loff_t end)
-{
- struct page *page;
-
- page = dax_layout_busy_page_range(inode->i_mapping, start, end);
- if (!page)
- return 0;
-
- *retry = true;
- return dax_wait_page_idle(page, fuse_wait_dax_page, inode);
-}
-
+/* Should be called with mapping->invalidate_lock held exclusively. */
int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start,
u64 dmap_end)
{
- bool retry;
- int ret;
-
- do {
- retry = false;
- ret = __fuse_dax_break_layouts(inode, &retry, dmap_start,
- dmap_end);
- } while (ret == 0 && retry);
-
- return ret;
+ return dax_break_layout(inode, dmap_start, dmap_end,
+ fuse_wait_dax_page);
}

ssize_t fuse_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 1b5613d..d4f07e0 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -2735,21 +2735,17 @@ xfs_mmaplock_two_inodes_and_break_dax_layout(
struct xfs_inode *ip2)
{
int error;
- bool retry;
struct page *page;

if (ip1->i_ino > ip2->i_ino)
swap(ip1, ip2);

again:
- retry = false;
/* Lock the first inode */
xfs_ilock(ip1, XFS_MMAPLOCK_EXCL);
- error = xfs_break_dax_layouts(VFS_I(ip1), &retry);
- if (error || retry) {
+ error = xfs_break_dax_layouts(VFS_I(ip1));
+ if (error) {
xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
- if (error == 0 && retry)
- goto again;
return error;
}

@@ -2764,7 +2760,7 @@ xfs_mmaplock_two_inodes_and_break_dax_layout(
* for this nested lock case.
*/
page = dax_layout_busy_page(VFS_I(ip2)->i_mapping);
- if (page && page_ref_count(page) != 1) {
+ if (!dax_page_is_idle(page)) {
xfs_iunlock(ip2, XFS_MMAPLOCK_EXCL);
xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
goto again;
@@ -3008,19 +3004,11 @@ xfs_wait_dax_page(

int
xfs_break_dax_layouts(
- struct inode *inode,
- bool *retry)
+ struct inode *inode)
{
- struct page *page;
-
xfs_assert_ilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL);

- page = dax_layout_busy_page(inode->i_mapping);
- if (!page)
- return 0;
-
- *retry = true;
- return dax_wait_page_idle(page, xfs_wait_dax_page, inode);
+ return dax_break_layout_inode(inode, xfs_wait_dax_page);
}

int
@@ -3038,8 +3026,8 @@ xfs_break_layouts(
retry = false;
switch (reason) {
case BREAK_UNMAP:
- error = xfs_break_dax_layouts(inode, &retry);
- if (error || retry)
+ error = xfs_break_dax_layouts(inode);
+ if (error)
break;
fallthrough;
case BREAK_WRITE:
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index c08093a..123dfa9 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -603,7 +603,7 @@ xfs_itruncate_extents(
return xfs_itruncate_extents_flags(tpp, ip, whichfork, new_size, 0);
}

-int xfs_break_dax_layouts(struct inode *inode, bool *retry);
+int xfs_break_dax_layouts(struct inode *inode);
int xfs_break_layouts(struct inode *inode, uint *iolock,
enum layout_break_reason reason);

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 9b1ce98..a6b277f 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -207,12 +207,9 @@ int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
const struct iomap_ops *ops);

-static inline int dax_wait_page_idle(struct page *page,
- void (cb)(struct inode *),
- struct inode *inode)
+static inline bool dax_page_is_idle(struct page *page)
{
- return ___wait_var_event(page, page_ref_count(page) == 1,
- TASK_INTERRUPTIBLE, 0, 0, cb(inode));
+ return page && page_ref_count(page) == 1;
}

#if IS_ENABLED(CONFIG_DAX)
@@ -228,6 +225,15 @@ static inline void dax_read_unlock(int id)
{
}
#endif /* CONFIG_DAX */
+
+#if !IS_ENABLED(CONFIG_FS_DAX)
+static inline int __must_check dax_break_layout(struct inode *inode,
+ loff_t start, loff_t end, void (cb)(struct inode *))
+{
+ return 0;
+}
+#endif
+
bool dax_alive(struct dax_device *dax_dev);
void *dax_get_private(struct dax_device *dax_dev);
long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
@@ -251,6 +257,13 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
pgoff_t index);
+int __must_check dax_break_layout(struct inode *inode, loff_t start,
+ loff_t end, void (cb)(struct inode *));
+static inline int __must_check dax_break_layout_inode(struct inode *inode,
+ void (cb)(struct inode *))
+{
+ return dax_break_layout(inode, 0, LLONG_MAX, cb);
+}
int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
struct inode *dest, loff_t destoff,
loff_t len, bool *is_same,
--
git-series 0.9.1