netdev - Re: [PATCH net 1/1] tipc: fix socket timer deadlock

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Message-Id: <20160617.215530.401735252835970579.davem@davemloft.net>
Date:	Fri, 17 Jun 2016 21:55:30 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jon.maloy@...csson.com
Cc:	netdev@...r.kernel.org, paul.gortmaker@...driver.com,
	parthasarathy.bhuvaragan@...csson.com, richard.alpe@...csson.com,
	ying.xue@...driver.com, maloy@...jonn.com,
	tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net 1/1] tipc: fix socket timer deadlock

From: Jon Maloy <jon.maloy@...csson.com>
Date: Fri, 17 Jun 2016 06:35:57 -0400

> We sometimes observe a 'deadly embrace' type deadlock occurring
> between mutually connected sockets on the same node. This happens
> when the one-hour peer supervision timers happen to expire
> simultaneously in both sockets.
> 
> The scenario is as follows:
 ...
> Further analysis reveals that there are three different locations in the
> socket code where tipc_sk_respond() is called within the context of the
> socket lock, with ensuing risk of similar deadlocks.
> 
> We now solve this by passing a buffer queue along with all upcalls where
> sk_lock.slock may potentially be held. Response or rejected message
> buffers are accumulated into this queue instead of being sent out
> directly, and only sent once we know we are safely outside the slock
> context.
> 
> Reported-by: GUNA <gbalasun@...il.com>
> Acked-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied, thanks Jon.