From: Miklos Szeredi <mszeredi@redhat.com>
Date: Wed, 23 Oct 2019 14:26:37 +0200
Subject: fuse: truncate pending writes on O_TRUNC
Git-commit: e4648309b85a78f8c787457832269a8712a8673e
Patch-mainline: v5.4-rc6
References: bsc#1175065

Make sure cached writes are not reordered around open(..., O_TRUNC), with
the obvious wrong results.

Fixes: 4d99ff8f12eb ("fuse: Turn writeback cache on")
Cc: <stable@vger.kernel.org> # v3.15+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/fuse/file.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 0f0225686aee..6edf949b9139 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -217,7 +217,7 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	int err;
-	bool lock_inode = (file->f_flags & O_TRUNC) &&
+	bool is_wb_truncate = (file->f_flags & O_TRUNC) &&
 			  fc->atomic_o_trunc &&
 			  fc->writeback_cache;
 
@@ -225,16 +225,20 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 	if (err)
 		return err;
 
-	if (lock_inode)
+	if (is_wb_truncate) {
 		inode_lock(inode);
+		fuse_set_nowrite(inode);
+	}
 
 	err = fuse_do_open(fc, get_node_id(inode), file, isdir);
 
 	if (!err)
 		fuse_finish_open(inode, file);
 
-	if (lock_inode)
+	if (is_wb_truncate) {
+		fuse_release_nowrite(inode);
 		inode_unlock(inode);
+	}
 
 	return err;
 }