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nbd: Reclassify sockets to avoid lockdep circular dependency

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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: ffa1e7ada4 ("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 <edumazet@google.com>
Link: https://patch.msgid.link/20260613042619.1108126-1-edumazet@google.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Eric Dumazet
2026-06-13 04:26:19 +00:00
committed by Jens Axboe
parent e8dcf2d142
commit d532cddb6c
1 changed files with 37 additions and 0 deletions
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37
drivers/block/nbd.c
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@@ -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