[v7,01/20] fuse: Fix dax truncate/punch_hole fault path

Commit Message

Alistair Popple Feb. 4, 2025, 10:47 p.m. UTC

FS DAX requires file systems to call into the DAX layout prior to unlinking
inodes to ensure there is no ongoing DMA or other remote access to the
direct mapped page. The fuse file system implements
fuse_dax_break_layouts() to do this which includes a comment indicating
that passing dmap_end == 0 leads to unmapping of the whole file.

However this is not true - passing dmap_end == 0 will not unmap anything
before dmap_start, and further more dax_layout_busy_page_range() will not
scan any of the range to see if there maybe ongoing DMA access to the
range. Fix this by passing -1 for dmap_end to fuse_dax_break_layouts()
which will invalidate the entire file range to
dax_layout_busy_page_range().

Signed-off-by: Alistair Popple <[e-mail]>
Co-developed-by: Dan Williams <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>
Fixes: 6ae330cad6ef ("virtiofs: serialize truncate/punch_hole and dax fault path")
Cc: Vivek Goyal <[e-mail]>

---

Changes for v6:

 - Original patch had a misplaced hunk due to a bad rebase.
 - Reworked fix based on Dan's comments.
---
 fs/fuse/dax.c  | 1 -
 fs/fuse/dir.c  | 2 +-
 fs/fuse/file.c | 4 ++--
 3 files changed, 3 insertions(+), 4 deletions(-)

Comments

Balbir Singh Feb. 5, 2025, 3:07 a.m. UTC | #1

On 2/5/25 09:47, Alistair Popple wrote:
> FS DAX requires file systems to call into the DAX layout prior to unlinking
> inodes to ensure there is no ongoing DMA or other remote access to the
> direct mapped page. The fuse file system implements
> fuse_dax_break_layouts() to do this which includes a comment indicating
> that passing dmap_end == 0 leads to unmapping of the whole file.
> 
> However this is not true - passing dmap_end == 0 will not unmap anything
> before dmap_start, and further more dax_layout_busy_page_range() will not
> scan any of the range to see if there maybe ongoing DMA access to the
> range. Fix this by passing -1 for dmap_end to fuse_dax_break_layouts()
> which will invalidate the entire file range to
> dax_layout_busy_page_range().
> 
> Signed-off-by: Alistair Popple <[e-mail]>
> Co-developed-by: Dan Williams <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>
> Fixes: 6ae330cad6ef ("virtiofs: serialize truncate/punch_hole and dax fault path")
> Cc: Vivek Goyal <[e-mail]>
> 

Looks good

Reviewed-by: Balbir Singh <[e-mail]>

Patch

diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
index 0b6ee6d..b7f805d 100644
--- a/fs/fuse/dax.c
+++ b/fs/fuse/dax.c
@@ -682,7 +682,6 @@  static int __fuse_dax_break_layouts(struct inode *inode, bool *retry,
 			0, 0, fuse_wait_dax_page(inode));
 }
 
-/* dmap_end == 0 leads to unmapping of whole file */
 int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start,
 				  u64 dmap_end)
 {
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 198862b..6c5d441 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1940,7 +1940,7 @@  int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	if (FUSE_IS_DAX(inode) && is_truncate) {
 		filemap_invalidate_lock(mapping);
 		fault_blocked = true;
-		err = fuse_dax_break_layouts(inode, 0, 0);
+		err = fuse_dax_break_layouts(inode, 0, -1);
 		if (err) {
 			filemap_invalidate_unlock(mapping);
 			return err;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 7d92a54..dc90613 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -253,7 +253,7 @@  static int fuse_open(struct inode *inode, struct file *file)
 
 	if (dax_truncate) {
 		filemap_invalidate_lock(inode->i_mapping);
-		err = fuse_dax_break_layouts(inode, 0, 0);
+		err = fuse_dax_break_layouts(inode, 0, -1);
 		if (err)
 			goto out_inode_unlock;
 	}
@@ -3196,7 +3196,7 @@  static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
 	inode_lock(inode);
 	if (block_faults) {
 		filemap_invalidate_lock(inode->i_mapping);
-		err = fuse_dax_break_layouts(inode, 0, 0);
+		err = fuse_dax_break_layouts(inode, 0, -1);
 		if (err)
 			goto out;
 	}