This is a note to let you know that I've just added the patch titled
fs: factor out a direct_write_fallback helper
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-factor-out-a-direct_write_fallback-helper.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From [email protected] Tue Oct 21 16:17:20
>2025
From: Mahmoud Adam <[email protected]>
Date: Tue, 21 Oct 2025 09:03:39 +0200
Subject: fs: factor out a direct_write_fallback helper
To: <[email protected]>
Cc: <[email protected]>, <[email protected]>, Christoph Hellwig
<[email protected]>, Damien Le Moal <[email protected]>, Miklos Szeredi
<[email protected]>, "Darrick J. Wong" <[email protected]>, Al Viro
<[email protected]>, Andreas Gruenbacher <[email protected]>, "Anna
Schumaker" <[email protected]>, Chao Yu <[email protected]>, Christian Brauner
<[email protected]>, Hannes Reinecke <[email protected]>, Ilya Dryomov
<[email protected]>, Jaegeuk Kim <[email protected]>, Jens Axboe
<[email protected]>, Johannes Thumshirn <[email protected]>, "Matthew
Wilcox" <[email protected]>, Miklos Szeredi <[email protected]>, "Theodore
Ts'o" <[email protected]>, Trond Myklebust <[email protected]>, Xiubo
Li <[email protected]>, Andrew Morton <[email protected]>, "Jeff
Layton" <[email protected]>, Andreas Dilger <[email protected]>,
Christoph Hellwig <[email protected]>, Ryusuke Konishi
<[email protected]>, Luis Chamberlain <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>
Message-ID: <[email protected]>
From: Christoph Hellwig <[email protected]>
commit 44fff0fa08ec5a6d9d5fb05443a36d854d0ece4d upstream.
Add a helper dealing with handling the syncing of a buffered write
fallback for direct I/O.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Miklos Szeredi <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andreas Gruenbacher <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Chao Yu <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Ilya Dryomov <[email protected]>
Cc: Jaegeuk Kim <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Johannes Thumshirn <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Xiubo Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
[backing_dev_info still being used here. do small changes to the patch
to keep the out label. Which means replacing all returns to goto out.]
Signed-off-by: Mahmoud Adam <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/libfs.c | 41 +++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 +
mm/filemap.c | 61 ++++++++++++-----------------------------------------
3 files changed, 57 insertions(+), 47 deletions(-)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1582,3 +1582,44 @@ bool inode_maybe_inc_iversion(struct ino
return true;
}
EXPORT_SYMBOL(inode_maybe_inc_iversion);
+
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+ ssize_t direct_written, ssize_t buffered_written)
+{
+ struct address_space *mapping = iocb->ki_filp->f_mapping;
+ loff_t pos = iocb->ki_pos - buffered_written;
+ loff_t end = iocb->ki_pos - 1;
+ int err;
+
+ /*
+ * If the buffered write fallback returned an error, we want to return
+ * the number of bytes which were written by direct I/O, or the error
+ * code if that was zero.
+ *
+ * Note that this differs from normal direct-io semantics, which will
+ * return -EFOO even if some bytes were written.
+ */
+ if (unlikely(buffered_written < 0)) {
+ if (direct_written)
+ return direct_written;
+ return buffered_written;
+ }
+
+ /*
+ * We need to ensure that the page cache pages are written to disk and
+ * invalidated to preserve the expected O_DIRECT semantics.
+ */
+ err = filemap_write_and_wait_range(mapping, pos, end);
+ if (err < 0) {
+ /*
+ * We don't know how much we wrote, so just return the number of
+ * bytes which were direct-written
+ */
+ if (direct_written)
+ return direct_written;
+ return err;
+ }
+ invalidate_mapping_pages(mapping, pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
+ return direct_written + buffered_written;
+}
+EXPORT_SYMBOL_GPL(direct_write_fallback);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3278,6 +3278,8 @@ extern ssize_t __generic_file_write_iter
extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
ssize_t generic_perform_write(struct kiocb *, struct iov_iter *);
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+ ssize_t direct_written, ssize_t buffered_written);
ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
rwf_t flags);
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3923,25 +3923,21 @@ ssize_t __generic_file_write_iter(struct
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
- struct inode *inode = mapping->host;
- ssize_t written = 0;
- ssize_t err;
- ssize_t status;
+ struct inode *inode = mapping->host;
+ ssize_t ret;
/* We can write back this queue in page reclaim */
current->backing_dev_info = inode_to_bdi(inode);
- err = file_remove_privs(file);
- if (err)
+ ret = file_remove_privs(file);
+ if (ret)
goto out;
- err = file_update_time(file);
- if (err)
+ ret = file_update_time(file);
+ if (ret)
goto out;
if (iocb->ki_flags & IOCB_DIRECT) {
- loff_t pos, endbyte;
-
- written = generic_file_direct_write(iocb, from);
+ ret = generic_file_direct_write(iocb, from);
/*
* If the write stopped short of completing, fall back to
* buffered writes. Some filesystems do this for writes to
@@ -3949,46 +3945,17 @@ ssize_t __generic_file_write_iter(struct
* not succeed (even if it did, DAX does not handle dirty
* page-cache pages correctly).
*/
- if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
- goto out;
-
- pos = iocb->ki_pos;
- status = generic_perform_write(iocb, from);
- /*
- * If generic_perform_write() returned a synchronous error
- * then we want to return the number of bytes which were
- * direct-written, or the error code if that was zero. Note
- * that this differs from normal direct-io semantics, which
- * will return -EFOO even if some bytes were written.
- */
- if (unlikely(status < 0)) {
- err = status;
+ if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
goto out;
- }
- /*
- * We need to ensure that the page cache pages are written to
- * disk and invalidated to preserve the expected O_DIRECT
- * semantics.
- */
- endbyte = pos + status - 1;
- err = filemap_write_and_wait_range(mapping, pos, endbyte);
- if (err == 0) {
- written += status;
- invalidate_mapping_pages(mapping,
- pos >> PAGE_SHIFT,
- endbyte >> PAGE_SHIFT);
- } else {
- /*
- * We don't know how much we wrote, so just return
- * the number of bytes which were direct-written
- */
- }
- } else {
- written = generic_perform_write(iocb, from);
+ ret = direct_write_fallback(iocb, from, ret,
+ generic_perform_write(iocb, from));
+ goto out;
}
+
+ ret = generic_perform_write(iocb, from);
out:
current->backing_dev_info = NULL;
- return written ? written : err;
+ return ret;
}
EXPORT_SYMBOL(__generic_file_write_iter);
Patches currently in stable-queue which might be from [email protected] are
queue-6.1/block-fix-race-between-set_blocksize-and-read-paths.patch
queue-6.1/filemap-add-a-kiocb_invalidate_pages-helper.patch
queue-6.1/fs-factor-out-a-direct_write_fallback-helper.patch
queue-6.1/direct_write_fallback-on-error-revert-the-ki_pos-update-from-buffered-write.patch
queue-6.1/filemap-update-ki_pos-in-generic_perform_write.patch
queue-6.1/filemap-add-a-kiocb_invalidate_post_direct_write-helper.patch
queue-6.1/nilfs2-fix-deadlock-warnings-caused-by-lock-dependency-in-init_nilfs.patch
queue-6.1/block-open-code-__generic_file_write_iter-for-blkdev-writes.patch
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