fuse: fix wrong ff->iomode state changes from parallel dio write

There is a confusion with fuse_file_uncached_io_{start,end} interface.
These helpers do two things when called from passthrough open()/release():
1. Take/drop negative refcount of fi->iocachectr (inode uncached io mode)
2. State change ff->iomode IOM_NONE <-> IOM_UNCACHED (file uncached open)

The calls from parallel dio write path need to take a reference on
fi->iocachectr, but they should not be changing ff->iomode state, because
in this case, the fi->iocachectr reference does not stick around until file
release().

Factor out helpers fuse_inode_uncached_io_{start,end}, to be used from
parallel dio write path and rename fuse_file_*cached_io_{start,end} helpers
to fuse_file_*cached_io_{open,release} to clarify the difference.

Fixes: 205c1d8026 ("fuse: allow parallel dio writes with FUSE_DIRECT_IO_ALLOW_MMAP")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -1362,7 +1362,7 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 			  bool *exclusive)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
-	struct fuse_file *ff = iocb->ki_filp->private_data;
+	struct fuse_inode *fi = get_fuse_inode(inode);
 
 	*exclusive = fuse_dio_wr_exclusive_lock(iocb, from);
 	if (*exclusive) {
@@ -1377,7 +1377,7 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 		 * have raced, so check it again.
 		 */
 		if (fuse_io_past_eof(iocb, from) ||
-		    fuse_file_uncached_io_start(inode, ff, NULL) != 0) {
+		    fuse_inode_uncached_io_start(fi, NULL) != 0) {
 			inode_unlock_shared(inode);
 			inode_lock(inode);
 			*exclusive = true;
@@ -1388,13 +1388,13 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 static void fuse_dio_unlock(struct kiocb *iocb, bool exclusive)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
-	struct fuse_file *ff = iocb->ki_filp->private_data;
+	struct fuse_inode *fi = get_fuse_inode(inode);
 
 	if (exclusive) {
 		inode_unlock(inode);
 	} else {
 		/* Allow opens in caching mode after last parallel dio end */
-		fuse_file_uncached_io_end(inode, ff);
+		fuse_inode_uncached_io_end(fi);
 		inode_unlock_shared(inode);
 	}
 }
@@ -2574,8 +2574,10 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 		 * First mmap of direct_io file enters caching inode io mode.
 		 * Also waits for parallel dio writers to go into serial mode
 		 * (exclusive instead of shared lock).
+		 * After first mmap, the inode stays in caching io mode until
+		 * the direct_io file release.
 		 */
-		rc = fuse_file_cached_io_start(inode, ff);
+		rc = fuse_file_cached_io_open(inode, ff);
 		if (rc)
 			return rc;
 	}

fs/fuse/fuse_i.h

@@ -1394,9 +1394,10 @@ int fuse_fileattr_set(struct mnt_idmap *idmap,
 		      struct dentry *dentry, struct fileattr *fa);
 
 /* iomode.c */
-int fuse_file_cached_io_start(struct inode *inode, struct fuse_file *ff);
+int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff);
-int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff, struct fuse_backing *fb);
+int fuse_inode_uncached_io_start(struct fuse_inode *fi,
-void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff);
+				 struct fuse_backing *fb);
+void fuse_inode_uncached_io_end(struct fuse_inode *fi);
 
 int fuse_file_io_open(struct file *file, struct inode *inode);
 void fuse_file_io_release(struct fuse_file *ff, struct inode *inode);

fs/fuse/inode.c

@@ -175,6 +175,7 @@ static void fuse_evict_inode(struct inode *inode)
 		}
 	}
 	if (S_ISREG(inode->i_mode) && !fuse_is_bad(inode)) {
+		WARN_ON(fi->iocachectr != 0);
 		WARN_ON(!list_empty(&fi->write_files));
 		WARN_ON(!list_empty(&fi->queued_writes));
 	}

fs/fuse/iomode.c

@@ -21,12 +21,13 @@ static inline bool fuse_is_io_cache_wait(struct fuse_inode *fi)
 }
 
 /*
- * Start cached io mode.
+ * Called on cached file open() and on first mmap() of direct_io file.
+ * Takes cached_io inode mode reference to be dropped on file release.
  *
  * 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)
+int fuse_file_cached_io_open(struct inode *inode, struct fuse_file *ff)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
 
@@ -67,10 +68,9 @@ int fuse_file_cached_io_start(struct inode *inode, struct fuse_file *ff)
 	return 0;
 }
 
-static void fuse_file_cached_io_end(struct inode *inode, struct fuse_file *ff)
+static void fuse_file_cached_io_release(struct fuse_file *ff,
+					struct fuse_inode *fi)
 {
-	struct fuse_inode *fi = get_fuse_inode(inode);
-
 	spin_lock(&fi->lock);
 	WARN_ON(fi->iocachectr <= 0);
 	WARN_ON(ff->iomode != IOM_CACHED);
@@ -82,9 +82,8 @@ 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 */
-int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff, struct fuse_backing *fb)
+int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
 {
-	struct fuse_inode *fi = get_fuse_inode(inode);
 	struct fuse_backing *oldfb;
 	int err = 0;
 
@@ -99,9 +98,7 @@ int fuse_file_uncached_io_start(struct inode *inode, struct fuse_file *ff, struc
 		err = -ETXTBSY;
 		goto unlock;
 	}
-	WARN_ON(ff->iomode != IOM_NONE);
 	fi->iocachectr--;
-	ff->iomode = IOM_UNCACHED;
 
 	/* fuse inode holds a single refcount of backing file */
 	if (!oldfb) {
@@ -115,15 +112,29 @@ unlock:
 	return err;
 }
 
-void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
+/* Takes uncached_io inode mode reference to be dropped on file release */
+static int fuse_file_uncached_io_open(struct inode *inode,
+				      struct fuse_file *ff,
+				      struct fuse_backing *fb)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
+	int err;
+
+	err = fuse_inode_uncached_io_start(fi, fb);
+	if (err)
+		return err;
+
+	WARN_ON(ff->iomode != IOM_NONE);
+	ff->iomode = IOM_UNCACHED;
+	return 0;
+}
+
+void fuse_inode_uncached_io_end(struct fuse_inode *fi)
+{
 	struct fuse_backing *oldfb = NULL;
 
 	spin_lock(&fi->lock);
 	WARN_ON(fi->iocachectr >= 0);
-	WARN_ON(ff->iomode != IOM_UNCACHED);
-	ff->iomode = IOM_NONE;
 	fi->iocachectr++;
 	if (!fi->iocachectr) {
 		wake_up(&fi->direct_io_waitq);
@@ -134,6 +145,15 @@ void fuse_file_uncached_io_end(struct inode *inode, struct fuse_file *ff)
 		fuse_backing_put(oldfb);
 }
 
+/* Drop uncached_io reference from passthrough open */
+static void fuse_file_uncached_io_release(struct fuse_file *ff,
+					  struct fuse_inode *fi)
+{
+	WARN_ON(ff->iomode != IOM_UNCACHED);
+	ff->iomode = IOM_NONE;
+	fuse_inode_uncached_io_end(fi);
+}
+
 /*
  * Open flags that are allowed in combination with FOPEN_PASSTHROUGH.
  * A combination of FOPEN_PASSTHROUGH and FOPEN_DIRECT_IO means that read/write
@@ -163,7 +183,7 @@ static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
 		return PTR_ERR(fb);
 
 	/* First passthrough file open denies caching inode io mode */
-	err = fuse_file_uncached_io_start(inode, ff, fb);
+	err = fuse_file_uncached_io_open(inode, ff, fb);
 	if (!err)
 		return 0;
 
@@ -216,7 +236,7 @@ int fuse_file_io_open(struct file *file, struct inode *inode)
 	if (ff->open_flags & FOPEN_PASSTHROUGH)
 		err = fuse_file_passthrough_open(inode, file);
 	else
-		err = fuse_file_cached_io_start(inode, ff);
+		err = fuse_file_cached_io_open(inode, ff);
 	if (err)
 		goto fail;
 
@@ -236,8 +256,10 @@ fail:
 /* No more pending io and no new io possible to inode via open/mmapped file */
 void fuse_file_io_release(struct fuse_file *ff, struct inode *inode)
 {
+	struct fuse_inode *fi = get_fuse_inode(inode);
+
 	/*
-	 * Last parallel dio close allows caching inode io mode.
+	 * Last passthrough file close allows caching inode io mode.
 	 * Last caching file close exits caching inode io mode.
 	 */
 	switch (ff->iomode) {
@@ -245,10 +267,10 @@ void fuse_file_io_release(struct fuse_file *ff, struct inode *inode)
 		/* Nothing to do */
 		break;
 	case IOM_UNCACHED:
-		fuse_file_uncached_io_end(inode, ff);
+		fuse_file_uncached_io_release(ff, fi);
 		break;
 	case IOM_CACHED:
-		fuse_file_cached_io_end(inode, ff);
+		fuse_file_cached_io_release(ff, fi);
 		break;
 	}
 }