[PATCH 12/15] fs: move kiocb_start_write() into vfs_iocb_iter_write()

[Amir Goldstein <amir73il@gmail.com>]

In vfs code, sb_start_write() is usually called after the permission hook
in rw_verify_area().  vfs_iocb_iter_write() is an exception to this rule,
where kiocb_start_write() is called by its callers.

Move kiocb_start_write() from the callers into vfs_iocb_iter_write()
after the rw_verify_area() checks, to make them "start-write-safe".

This is needed for fanotify "pre content" events.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/cachefiles/io.c  | 2 --
 fs/overlayfs/file.c | 1 -
 fs/read_write.c     | 2 ++
 3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 009d23cd435b..3d3667807636 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -319,8 +319,6 @@ int __cachefiles_write(struct cachefiles_object *object,
 		ki->iocb.ki_complete = cachefiles_write_complete;
 	atomic_long_add(ki->b_writing, &cache->b_writing);
 
-	kiocb_start_write(&ki->iocb);
-
 	get_file(ki->iocb.ki_filp);
 	cachefiles_grab_object(object, cachefiles_obj_get_ioreq);
 
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 690b173f34fc..2adf3a5641cd 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -456,7 +456,6 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 		aio_req->iocb.ki_flags = ifl;
 		aio_req->iocb.ki_complete = ovl_aio_queue_completion;
 		refcount_set(&aio_req->ref, 2);
-		kiocb_start_write(&aio_req->iocb);
 		ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
 		ovl_aio_put(aio_req);
 		if (ret != -EIOCBQUEUED)
diff --git a/fs/read_write.c b/fs/read_write.c
index 5b18e13c2620..8d381929701c 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -854,6 +854,7 @@ static ssize_t do_iter_write(struct file *file, struct iov_iter *iter,
 		return do_loop_readv_writev(file, iter, pos, WRITE, flags);
 }
 
+/* Caller is responsible for calling kiocb_end_write() on completion */
 ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
 			    struct iov_iter *iter)
 {
@@ -874,6 +875,7 @@ ssize_t vfs_iocb_iter_write(struct file *file, struct kiocb *iocb,
 	if (ret < 0)
 		return ret;
 
+	kiocb_start_write(iocb);
 	ret = call_write_iter(file, iocb, iter);
 	if (ret > 0)
 		fsnotify_modify(file);
-- 
2.34.1