netdev - Re: [PATCH v4] ipx: fix locking regression in ipx_sendmsg and ipx

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Date:	Wed, 19 Nov 2014 23:12:21 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Jiri Bohac <jbohac@...e.cz>
Cc:	David Miller <davem@...emloft.net>, acme@...stprotocols.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH v4] ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg

On Wednesday 19 November 2014 23:05:49 Jiri Bohac wrote:
> This fixes an old regression introduced by commit
> b0d0d915 (ipx: remove the BKL).
> 
> When a recvmsg syscall blocks waiting for new data, no data can be sent on the
> same socket with sendmsg because ipx_recvmsg() sleeps with the socket locked.
> 
> This breaks mars-nwe (NetWare emulator):
> - the ncpserv process reads the request using recvmsg
> - ncpserv forks and spawns nwconn
> - ncpserv calls a (blocking) recvmsg and waits for new requests
> - nwconn deadlocks in sendmsg on the same socket 
> 
> Commit b0d0d915 has simply replaced BKL locking with
> lock_sock/release_sock. Unlike now, BKL got unlocked while
> sleeping, so a blocking recvmsg did not block a concurrent
> sendmsg.
> 
> Only keep the socket locked while actually working with the socket data and
> release it prior to calling skb_recv_datagram(). 
> 
> 
> Signed-off-by: Jiri Bohac <jbohac@...e.cz>
> 

Reviewed-by: Arnd Bergmann <arnd@...db.de>
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