[PATCH v3 3/7] fs: create kiocb_{start,end}_write() helpers

[Amir Goldstein <amir73il@gmail.com>]

aio, io_uring, cachefiles and overlayfs, all open code an ugly variant
of file_{start,end}_write() to silence lockdep warnings.

Create helpers for this lockdep dance so we can use the helpers in all
the callers.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 include/linux/fs.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ced388aff51f..2548048a6e6c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2579,6 +2579,42 @@ static inline void file_end_write(struct file *file)
 	sb_end_write(file_inode(file)->i_sb);
 }
 
+/**
+ * kiocb_start_write - get write access to a superblock for async file io
+ * @iocb: the io context we want to submit the write with
+ *
+ * This is a variant of sb_start_write() for async io submission.
+ * Should be matched with a call to kiocb_end_write().
+ */
+static inline void kiocb_start_write(struct kiocb *iocb)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	sb_start_write(inode->i_sb);
+	/*
+	 * Fool lockdep by telling it the lock got released so that it
+	 * doesn't complain about the held lock when we return to userspace.
+	 */
+	__sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);
+}
+
+/**
+ * kiocb_end_write - drop write access to a superblock after async file io
+ * @iocb: the io context we sumbitted the write with
+ *
+ * Should be matched with a call to kiocb_start_write().
+ */
+static inline void kiocb_end_write(struct kiocb *iocb)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	/*
+	 * Tell lockdep we inherited freeze protection from submission thread.
+	 */
+	__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
+	sb_end_write(inode->i_sb);
+}
+
 /*
  * This is used for regular files where some users -- especially the
  * currently executed binary in a process, previously handled via
-- 
2.34.1