From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 17 Aug 2021 21:05:16 +0200
Subject: fuse: truncate pagecache on atomic_o_trunc
Git-commit: 76224355db7570cbe6b6f75c8929a1558828dd55
Patch-mainline: v5.15-rc1
References: bsc#1191051

fuse_finish_open() will be called with FUSE_NOWRITE in case of atomic
O_TRUNC.  This can deadlock with fuse_wait_on_page_writeback() in
fuse_launder_page() triggered by invalidate_inode_pages2().

Fix by replacing invalidate_inode_pages2() in fuse_finish_open() with a
truncate_pagecache() call.  This makes sense regardless of FOPEN_KEEP_CACHE
or fc->writeback cache, so do it unconditionally.

Reported-by: Xie Yongji <xieyongji@bytedance.com>
Reported-and-tested-by: syzbot+bea44a5189836d956894@syzkaller.appspotmail.com
Fixes: e4648309b85a ("fuse: truncate pending writes on O_TRUNC")
Cc: <stable@vger.kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: Luis Henriques <lhenriques@suse.com>

---
 fs/fuse/file.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -177,10 +177,9 @@ void fuse_finish_open(struct inode *inod
 
 	if (ff->open_flags & FOPEN_DIRECT_IO)
 		file->f_op = &fuse_direct_io_file_operations;
-	if (!(ff->open_flags & FOPEN_KEEP_CACHE))
-		invalidate_inode_pages2(inode->i_mapping);
 	if (ff->open_flags & FOPEN_NONSEEKABLE)
 		nonseekable_open(inode, file);
+
 	if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC)) {
 		struct fuse_inode *fi = get_fuse_inode(inode);
 
@@ -188,10 +187,14 @@ void fuse_finish_open(struct inode *inod
 		fi->attr_version = ++fc->attr_version;
 		i_size_write(inode, 0);
 		spin_unlock(&fc->lock);
+		truncate_pagecache(inode, 0);
 		fuse_invalidate_attr(inode);
 		if (fc->writeback_cache)
 			file_update_time(file);
+	} else if (!(ff->open_flags & FOPEN_KEEP_CACHE)) {
+		invalidate_inode_pages2(inode->i_mapping);
 	}
+
 	if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
 		fuse_link_write_file(file);
 }