netdev - Re: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq

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Date: Thu, 29 Jun 2023 11:49:09 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Chengfeng Ye <dg573847474@...il.com>, marcelo.leitner@...il.com, 
 lucien.xin@...il.com, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org
Cc: linux-sctp@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sctp: fix potential deadlock on &net->sctp.addr_wq_lock

On Tue, 2023-06-27 at 12:03 +0000, Chengfeng Ye wrote:
> As &net->sctp.addr_wq_lock is also acquired by the timer
> sctp_addr_wq_timeout_handler() in protocal.c, the same lock acquisition
> at sctp_auto_asconf_init() seems should disable irq since it is called
> from sctp_accept() under process context.
> 
> Possible deadlock scenario:
> sctp_accept()
>     -> sctp_sock_migrate()
>     -> sctp_auto_asconf_init()
>     -> spin_lock(&net->sctp.addr_wq_lock)
>         <timer interrupt>
>         -> sctp_addr_wq_timeout_handler()
>         -> spin_lock_bh(&net->sctp.addr_wq_lock); (deadlock here)
> 
> This flaw was found using an experimental static analysis tool we are
> developing for irq-related deadlock.
> 
> The tentative patch fix the potential deadlock by spin_lock_bh().

Patch LGTM.

Please note that the above suggests a possible net-next follow-
up/cleanup, replacing the spin_lock_bh() in
sctp_addr_wq_timeout_handler() with a simple/faster spin_lock() - since
sctp_addr_wq_timeout_handler() runs with BH disabled. Anyhow net-next
is closed now, it will have to wait a bit ;)

Cheers,

Paolo