netdev - Re: [PATCH v3] fix locking regression in ipx_sendmsg and ipx

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Date:	Wed, 19 Nov 2014 17:38:13 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Jiri Bohac <jbohac@...e.cz>, Arnd Bergmann <arnd@...db.de>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH v3] fix locking regression in ipx_sendmsg and ipx_recvmsg

Hello.

On 11/19/2014 1:38 PM, 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>

> diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c
> index a0c7536..d0725d9 100644
> --- a/net/ipx/af_ipx.c
> +++ b/net/ipx/af_ipx.c
> @@ -1764,6 +1764,7 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock,
>   	struct ipxhdr *ipx = NULL;
>   	struct sk_buff *skb;
>   	int copied, rc;
> +	int locked = 1;

    Why not *bool*?

[...]

WBR, Sergei

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