fuse: truncate pagecache on atomic_o_trunc

mainline inclusion
from mainline-5.14
commit 76224355
category: bugfix
bugzilla: 181107
CVE: NA
---------------------------

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: e4648309 ("fuse: truncate pending writes on O_TRUNC")
Cc: <stable@vger.kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Conflict: fs/fuse/file.c
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>