fuse: allow parallel dio writes with FUSE_DIRECT_IO_ALLOW_MMAP

Instead of denying caching mode on parallel dio open, deny caching
open only while parallel dio are in-progress and wait for in-progress
parallel dio writes before entering inode caching io mode.

This allows executing parallel dio when inode is not in caching mode
even if shared mmap is allowed, but no mmaps have been performed on
the inode in question.

An mmap on direct_io file now waits for all in-progress parallel dio
writes to complete, so parallel dio writes together with
FUSE_DIRECT_IO_ALLOW_MMAP is enabled by this commit.

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 30 insertions, 18 deletions

diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
index a1a836b2aacc..ea47c76b9df1 100644
--- a/fs/fuse/iomode.c
+++ b/fs/fuse/iomode.c
@@ -13,21 +13,37 @@
 #include <linux/fs.h>
 
 /*
- * Start cached io mode, where parallel dio writes are not allowed.
+ * Return true if need to wait for new opens in caching mode.
+ */
+static inline bool fuse_is_io_cache_wait(struct fuse_inode *fi)
+{
+	return READ_ONCE(fi->iocachectr) < 0;
+}
+
+/*
+ * Start cached io mode.
+ *
+ * Blocks new parallel dio writes and waits for the in-progress parallel dio
+ * writes to complete.
  */
 int fuse_file_cached_io_start(struct inode *inode, struct fuse_file *ff)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
-	int err = 0;
 
 	/* There are no io modes if server does not implement open */
 	if (!ff->release_args)
 		return 0;
 
 	spin_lock(&fi->lock);
-	if (fi->iocachectr < 0) {
-		err = -ETXTBSY;
-		goto unlock;
+	/*
+	 * Setting the bit advises new direct-io writes to use an exclusive
+	 * lock - without it the wait below might be forever.
+	 */
+	while (fuse_is_io_cache_wait(fi)) {
+		set_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
+		spin_unlock(&fi->lock);
+		wait_event(fi->direct_io_waitq, !fuse_is_io_cache_wait(fi));
+		spin_lock(&fi->lock);
 	}
 	WARN_ON(ff->iomode == IOM_UNCACHED);
 	if (ff->iomode == IOM_NONE) {
@@ -36,9 +52,8 @@ int fuse_file_cached_io_start(struct inode *inode, struct fuse_file *ff)
 			set_bit(FUSE_I_CACHE_IO_MODE, &fi->state);
 		fi->iocachectr++;
 	}
-unlock:
 	spin_unlock(&fi->lock);
-	return err;
+	return 0;
 }
 
 static void fuse_file_cached_io_end(struct inode *inode, struct fuse_file *ff)
@@ -56,7 +71,7 @@ static void fuse_file_cached_io_end(struct inode *inode, struct fuse_file *ff)
 }
 
 /* Start strictly uncached io mode where cache access is not allowed */
-static int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff)
+int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	int err = 0;
@@ -74,7 +89,7 @@ unlock:
 	return err;
 }
 
-static void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
+void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
 
@@ -83,6 +98,8 @@ static void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
 	WARN_ON(ff->iomode != IOM_UNCACHED);
 	ff->iomode = IOM_NONE;
 	fi->iocachectr++;
+	if (!fi->iocachectr)
+		wake_up(&fi->direct_io_waitq);
 	spin_unlock(&fi->lock);
 }
 
@@ -106,21 +123,16 @@ int fuse_file_io_open(struct file *file, struct inode *inode)
 		ff->open_flags &= ~FOPEN_PARALLEL_DIRECT_WRITES;
 
 	/*
-	 * First parallel dio open denies caching inode io mode.
 	 * First caching file open enters caching inode io mode.
 	 *
 	 * Note that if user opens a file open with O_DIRECT, but server did
 	 * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT,
 	 * so we put the inode in caching mode to prevent parallel dio.
 	 */
-	if (ff->open_flags & FOPEN_DIRECT_IO) {
-		if (ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES)
-			err = fuse_file_uncached_io_start(inode, ff);
-		else
-			return 0;
-	} else {
-		err = fuse_file_cached_io_start(inode, ff);
-	}
+	if (ff->open_flags & FOPEN_DIRECT_IO)
+		return 0;
+
+	err = fuse_file_cached_io_start(inode, ff);
 	if (err)
 		goto fail;