linux-kernel - [PATCH 2/2] FUSE: Mark super block defunc on force unmount

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Message-Id: <20220511113050.2.I103b609e957667ca427c689fd83990e6ab32f3dd@changeid>
Date:   Wed, 11 May 2022 11:30:57 +1000
From:   Daniil Lunev <dlunev@...omium.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Daniil Lunev <dlunev@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>
Subject: [PATCH 2/2] FUSE: Mark super block defunc on force unmount

Force unmount of FUSE severes the connection with the user space, even
if there are still open files. Subsequent remount tries to re-use the
superblock held by the open files, which is meaningless in the FUSE case
after disconnect - reused super block doesn't have userspace counterpart
attached to it and is incapable of doing any IO.

Signed-off-by: Daniil Lunev <dlunev@...omium.org>
---

 fs/fuse/inode.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 8c0665c5dff88..e2ad3c9b2d5c5 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -476,8 +476,15 @@ static void fuse_umount_begin(struct super_block *sb)
 {
 	struct fuse_conn *fc = get_fuse_conn_super(sb);
 
-	if (!fc->no_force_umount)
-		fuse_abort_conn(fc);
+	if (fc->no_force_umount)
+		return;
+
+	sb->s_defunc = true;
+	if (sb->s_bdi != &noop_backing_dev_info) {
+		bdi_put(sb->s_bdi);
+		sb->s_bdi = &noop_backing_dev_info;
+	}
+	fuse_abort_conn(fc);
 }
 
 static void fuse_send_destroy(struct fuse_mount *fm)
-- 
2.31.0