Re: [PATCH net-next] mptcp: fix deadlock in mptcp_close()

[Dan Carpenter <dan.carpenter@oracle.com>]

On Thu, May 05, 2022 at 01:50:01PM +0200, Paolo Abeni wrote:
> On Thu, 2022-05-05 at 14:03 +0300, Dan Carpenter wrote:
> > The mptcp_data_lock/unlock(sk) functions are taking the same spin lock
> > as the lock_sock()/release_sock() functions.  So we're already holding
> > the lock at this point and taking it again will lead to a deadlock.
> 
> Note that lock_sock() (and release_sock()) releases the relevant
> spinlock before completion. AFAICs the above deadlock is not possible.
> 

Oh.  Yeah.  You're right.  I had hard coded into my local copy of Smatch
that it took that lock.

	{"lock_sock_nested", LOCK,   spin_lock, 0, "&$->sk_lock.slock"},
	{"release_sock",     UNLOCK, spin_lock, 0, "&$->sk_lock.slock"},

But that's wrong...  It drops the lock as you say.

regards,
dan carpenter