Date: Tue, 16 Aug 2016 06:01:57 -0700 From: Randall Stewart <rrs@netflix.com> To: Hans Petter Selasky <hps@selasky.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r304218 - head/sys/netinet Message-ID: <272AD783-2988-4EE7-89A5-EC6FA1313122@netflix.com> In-Reply-To: <92a3cfc1-56bc-813f-dd12-ac19c66fd716@selasky.org> References: <201608161240.u7GCeuWS082118@repo.freebsd.org> <92a3cfc1-56bc-813f-dd12-ac19c66fd716@selasky.org>
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Sure
Let me add some comments for you. The idea her is that you pick-up a =
reference
to the PCB.. so it can=E2=80=99t be removed. Thus when you re-lock the =
INP you check the
dropped flag (just in case someone did get in).
Let me get that in comments.. (note thats also why when using this =
function you
have to use its companion function to drop the reference).
> On Aug 16, 2016, at 5:58 AM, Hans Petter Selasky <hps@selasky.org> =
wrote:
>=20
> 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);
>> +
>> +}
>=20
> Hi,
>=20
> Could you add some comments describing how it is considered safe to =
drop the INP write-lock and then pick it up again?
>=20
> 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?
>=20
> --HPS
--------
Randall Stewart
rrs@netflix.com
803-317-4952
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