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

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Message-Id: <20141121.144655.1028344293385336290.davem@davemloft.net>
Date:	Fri, 21 Nov 2014 14:46:55 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jbohac@...e.cz
Cc:	arnd@...db.de, acme@...stprotocols.net, netdev@...r.kernel.org
Subject: Re: [PATCH v4] ipx: fix locking regression in ipx_sendmsg and
 ipx_recvmsg

From: Jiri Bohac <jbohac@...e.cz>
Date: Wed, 19 Nov 2014 23:05:49 +0100

> 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>

Applied.
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