Re: [PATCH] nbd: Reclassify sockets to avoid lockdep circular dependency

[Hillf Danton]

On Sat, 13 Jun 2026 04:26:19 +0000 Eric Dumazet wrote:
> 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")

Given the Fixes tag, can you specify anything wrong that commit added?

> Reported-by: syzbot+607cdcf978b3e79da878@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/netdev/6a2cdafe.428ffe26.258b27.0161.GAE@xxxxxxxxxx/T/#u
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> ---