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

[Eric Dumazet]

On Sat, Jun 13, 2026 at 3:12 AM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
> 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?

Nothing 'wrong'.

This (good) commit allowed LOCKDEP to throw a warning and eventually
panic the box.

A Fixes: tag does not imply the patch was wrong.