netdev - Re: [net 1/1] tipc: fix lockdep warning during node delete

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Message-Id: <20181127.163132.16083522702492801.davem@davemloft.net>
Date:   Tue, 27 Nov 2018 16:31:32 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     donmalo99@...il.com
Cc:     netdev@...r.kernel.org, gordan.mihaljevic@...tech.com.au,
        tung.q.nguyen@...tech.com.au, hoang.h.le@...tech.com.au,
        jon.maloy@...csson.com, maloy@...jonn.com, xinl@...hat.com,
        ying.xue@...driver.com, tipc-discussion@...ts.sourceforge.net
Subject: Re: [net 1/1] tipc: fix lockdep warning during node delete

From: Jon Maloy <donmalo99@...il.com>
Date: Mon, 26 Nov 2018 12:26:14 -0500

> We see the following lockdep warning:
 ...
> The reason is that the node timer handler sometimes needs to delete a
> node which has been disconnected for too long. To do this, it grabs
> the lock 'node_list_lock', which may at the same time be held by the
> generic node cleanup function, tipc_node_stop(), during module removal.
> Since the latter is calling del_timer_sync() inside the same lock, we
> have a potential deadlock.
> 
> We fix this letting the timer cleanup function use spin_trylock()
> instead of just spin_lock(), and when it fails to grab the lock it
> just returns so that the timer handler can terminate its execution.
> This is safe to do, since tipc_node_stop() anyway is about to
> delete both the timer and the node instance.
> 
> Fixes: 6a939f365bdb ("tipc: Auto removal of peer down node instance")
> Acked-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied and queued up for -stable, thanks Jon.