From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next] af_unix: dont send SCM_CREDENTIALS by default
Date: Mon, 19 Sep 2011 17:02:04 +0200
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Cc: tim.c.chen@linux.intel.com, zheng.z.yan@intel.com,
	yanzheng@21cn.com, netdev@vger.kernel.org, sfr@canb.auug.org.au,
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To: David Miller <davem@davemloft.net>
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Le lundi 19 septembre 2011 =C3=A0 06:28 +0200, Eric Dumazet a =C3=A9cri=
t :
> Le dimanche 18 septembre 2011 =C3=A0 21:07 -0400, David Miller a =C3=A9=
crit :
> > Eric, please respin your patches against current net-next, thanks!
>=20
> Sure, here it is :
>=20
> Its a bit different, so I didnt add Tim 'Acked-by'
>=20
> [PATCH net-next] af_unix: dont send SCM_CREDENTIALS by default
>=20
> Since commit 7361c36c5224 (af_unix: Allow credentials to work across
> user and pid namespaces) af_unix performance dropped a lot.
>=20
> This is because we now take a reference on pid and cred in each write=
(),
> and release them in read(), usually done from another process,
> eventually from another cpu. This triggers false sharing.

> This patch includes SCM_CREDENTIALS information in a af_unix message/=
skb
> only if requested by the sender, [man 7 unix for details how to inclu=
de
> ancillary data using sendmsg() system call]
>=20
> Note: This might break buggy applications that expected SCM_CREDENTIA=
L
> from an unaware write() system call.


I appears udevd is such an application.

I am trying testing SOCK_PASSCRED flag and include SCM_CREDENTIALS if
set.