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From: Arnd Bergmann <arnd@arndb.de>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Networking <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>,
	linux-arch <linux-arch@vger.kernel.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	Eric Dumazet <edumazet@google.com>,
	Willem de Bruijn <willemb@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-hams@vger.kernel.org,
	Bluez mailing list <linux-bluetooth@vger.kernel.org>,
	linux-can@vger.kernel.org, dccp@vger.kernel.org,
	linux-wpan@vger.kernel.org, linux-sctp@vger.kernel.org,
	linux-x25@vger.kernel.org
Subject: Re: [PATCH net-next 1/3] net: rework SIOCGSTAMP ioctl handling
Date: Fri, 31 Aug 2018 12:31:23 +0200
Message-ID: <CAK8P3a2XTUZJUqGu6v=SZqcoJTqM3fgtDAWBnBopX3=4NJYcRA@mail.gmail.com> (raw)
In-Reply-To: <CAF=yD-J7-GumUmonrZt7s44e3bsjY2DCD6ZpmhtCx6FOBV5BNA@mail.gmail.com>

On Thu, Aug 30, 2018 at 10:10 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Wed, Aug 29, 2018 at 9:05 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > The SIOCGSTAMP/SIOCGSTAMPNS ioctl commands are implemented by many
> > socket protocol handlers, and all of those end up calling the same
> > sock_get_timestamp()/sock_get_timestampns() helper functions, which
> > results in a lot of duplicate code.
> >
> > With the introduction of 64-bit time_t on 32-bit architectures, this
> > gets worse, as we then need four different ioctl commands in each
> > socket protocol implementation.
> >
> > To simplify that, let's add a new .gettstamp() operation in
> > struct proto_ops, and move ioctl implementation into the common
> > sock_ioctl()/compat_sock_ioctl_trans() functions that these all go
> > through.
> >
> > We can reuse the sock_get_timestamp() implementation, but generalize
> > it so it can deal with both native and compat mode, as well as
> > timeval and timespec structures.
> >
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> This also will simplify fixing a recently reported race condition with
> sock_get_timestamp [1]. That calls sock_enable_timestamp, which
> modifies sk->sk_flags, without taking the socket lock. Currently some
> callers of sock_get_timestamp hold the lock (ax25, netrom, qrtr), many
> don't. See also how this patch removes the lock_sock in the netrom
> case. Moving the call to sock_gettstamp outside the protocol handlers
> will allow taking the lock inside the function.

I suppose it would be best to always take that lock then, rather than
removing the lock as my patch does at the moment.

> If this is the only valid implementation of .gettstamp, the indirect
> call could be avoided in favor of a simple branch.

I thought about that as well, but I could not come up with a
good way to encode the difference between socket protocols
that allow timestamping and those that don't.

I think ideally we would just call sock_gettstamp() unconditonally
on every socket, and have that function decide whether timestamps
make sense or not. The part I did not understand is which ones
actually want the timestamps or not. Most protocols that
implement the ioctls also assign skb->tstamp, but there are some
protocols in which I could not see skb->tstamp ever being set,
and some that set it but don't seem to have the ioctls.

Looking at it again, it seems that sock_gettstamp() should
actually deal with this gracefully: it will return a -EINVAL
error condition if the timestamp remains at the
SK_DEFAULT_STAMP initial value, which is probably
just as appropriate (or better) as the current -ENOTTY
default, and if we are actually recording timestamps, we
might just as well report them.

> Acked-by: Willem de Bruijn <willemb@google.com>

Thanks,

      Arnd

  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-29 12:59 Arnd Bergmann
2018-08-30 20:09 ` Willem de Bruijn
2018-08-31 10:31   ` Arnd Bergmann [this message]
2018-08-31 13:37     ` Willem de Bruijn
2018-08-31 14:00       ` Arnd Bergmann
2018-08-31 15:08         ` Willem de Bruijn
2018-09-13 12:28 ` Arnd Bergmann
2018-09-21  9:14 ` Stefan Schmidt
2019-04-16 20:32 Arnd Bergmann
2019-04-17  9:35 ` Neil Horman
2019-04-17 17:21   ` David Miller
2019-04-17 20:15     ` Neil Horman
2019-04-17  9:59 ` Marc Kleine-Budde
2019-04-17 14:46 ` Willem de Bruijn
2019-04-17 16:19   ` Arnd Bergmann
2019-04-17 18:16     ` Willem de Bruijn

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