From 0865733b84f5d5b149b8cc680acfe7805aee04f8 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 13 Jun 2026 04:26:19 +0000 Subject: [PATCH] nbd: Reclassify sockets to avoid lockdep circular dependency syzbot reported a possible circular locking dependency in udp_sendmsg() where fs_reclaim can be triggered while holding sk_lock, and fs_reclaim can eventually depend on another sk_lock (e.g., if NBD is used for swap or writeback and NBD uses TLS/TCP which acquires sk_lock). Since the UDP socket and the NBD TCP/TLS socket are different, this is a false positive. Fix this by reclassifying NBD sockets to a separate lock class when they are added to the NBD device. This is similar to what nvme-tcp and other network block devices do. Fixes: ffa1e7ada456 ("block: Make request_queue lockdep splats show up earlier") Reported-by: syzbot+607cdcf978b3e79da878@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a2cdafe.428ffe26.258b27.0161.GAE@google.com/T/#u Signed-off-by: Eric Dumazet --- drivers/block/nbd.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index fe63f3c55d0d9..0e2180e910c4e 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1238,6 +1238,42 @@ static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd, return sock; } +#ifdef CONFIG_DEBUG_LOCK_ALLOC +static struct lock_class_key nbd_key[3]; +static struct lock_class_key nbd_slock_key[3]; + +static void nbd_reclassify_socket(struct socket *sock) +{ + struct sock *sk = sock->sk; + + if (WARN_ON_ONCE(!sock_allow_reclassification(sk))) + return; + + switch (sk->sk_family) { + case AF_INET: + sock_lock_init_class_and_name(sk, "slock-AF_INET-NBD", + &nbd_slock_key[0], + "sk_lock-AF_INET-NBD", + &nbd_key[0]); + break; + case AF_INET6: + sock_lock_init_class_and_name(sk, "slock-AF_INET6-NBD", + &nbd_slock_key[1], + "sk_lock-AF_INET6-NBD", + &nbd_key[1]); + break; + case AF_UNIX: + sock_lock_init_class_and_name(sk, "slock-AF_UNIX-NBD", + &nbd_slock_key[2], + "sk_lock-AF_UNIX-NBD", + &nbd_key[2]); + break; + } +} +#else +static inline void nbd_reclassify_socket(struct socket *sock) {} +#endif + static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg, bool netlink) { @@ -1254,6 +1290,7 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg, sock = nbd_get_socket(nbd, arg, &err); if (!sock) return err; + nbd_reclassify_socket(sock); /* * We need to make sure we don't get any errant requests while we're