fuse: don't ignore errors from fuse_writepages_fill()

mainline inclusion
from mainline-v5.8-rc6
commit 7779b047
category: bugfix
bugzilla: 39163
CVE: NA

-------------------------------------------------

fuse_writepages() ignores some errors taken from fuse_writepages_fill() I
believe it is a bug: if .writepages is called with WB_SYNC_ALL it should
either guarantee that all data was successfully saved or return error.

Fixes: 26d614df ("fuse: Implement writepages callback")
Signed-off-by: NVasily Averin <vvs@virtuozzo.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/fuse/file.c

@@ -1936,10 +1936,8 @@ static int fuse_writepages(struct address_space *mapping,
 
 	err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
 	if (data.req) {
-		/* Ignore errors if we can write at least one page */
 		BUG_ON(!data.req->num_pages);
 		fuse_writepages_send(&data);
-		err = 0;
 	}
 	if (data.ff)
 		fuse_file_put(data.ff, false, false);