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Subject: Re: svn commit: r304218 - head/sys/netinet
To: Randall Stewart <rrs@FreeBSD.org>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org
References: <201608161240.u7GCeuWS082118@repo.freebsd.org>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <92a3cfc1-56bc-813f-dd12-ac19c66fd716@selasky.org>
Date: Tue, 16 Aug 2016 14:58:45 +0200
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On 08/16/16 14:40, Randall Stewart wrote:
> +int
> +tcp_inpinfo_lock_add(struct inpcb *inp)
> +{
> +	in_pcbref(inp);
> +	INP_WUNLOCK(inp);
> +	INP_INFO_RLOCK(&V_tcbinfo);
> +	INP_WLOCK(inp);
> +	if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
> +		return(1);
> +	}
> +	return(0);
> +
> +}

Hi,

Could you add some comments describing how it is considered safe to drop 
the INP write-lock and then pick it up again?

My first impression is that because you are dropping the inp lock, 
multiple threads can enter the code in question, leaving the window open 
to races?

--HPS