[CRIU] [PATCH 2/2] rst: only restore dgram socket queue once

[Tycho Andersen]

On Thu, Jul 23, 2015 at 03:30:50PM +0300, Pavel Emelyanov wrote:
> On 07/23/2015 02:51 AM, Tycho Andersen wrote:
> > In the case where there were multiple clients for a dgram socket, we were
> > restoring the queue for each client. Instead, we should pick one client and
> > she should restore the queue while the rest skip it.
> > 
> > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> > ---
> >  sk-unix.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/sk-unix.c b/sk-unix.c
> > index 6c9ec25..e72fcbb 100644
> > --- a/sk-unix.c
> > +++ b/sk-unix.c
> > @@ -638,6 +638,13 @@ struct unix_sk_info {
> >  	 * after listen() if the socket is in TCP_LISTEN.
> >  	 */
> >  	futex_t prepared;
> > +
> > +	/*
> > +	 * For DGRAM sockets with queues, we should only restore the queue
> > +	 * once although it may be open by more than one tid. This is the peer
> > +	 * that should do the queueing.
> > +	 */
> > +	u32 queuer;
> 
> How about just putting a SK_QUEUE_RESTORED flag on the peer's flag?

This won't work because there is a copy of the list for each process,
so every process will see that it needs to restore the queue.

> >  };
> >  
> >  #define USK_PAIR_MASTER		0x1
> > @@ -708,7 +715,7 @@ static int post_open_unix_sk(struct file_desc *d, int fd)
> >  		return -1;
> >  	}
> >  
> > -	if (restore_sk_queue(fd, peer->ue->id))
> > +	if (peer->queuer == ui->ue->ino && restore_sk_queue(fd, peer->ue->id))
> 
> There are more places that call restore_sk_queue(). The ones in open_unixsk_pair_master
> are OK, they are restoring queues for each other, but how about the call in
> open_unixsk_standalone()? Should we patch it as well?

open_unixsk_standalone only calls it when peer is NULL, so we can't do
this check (although perhaps we could invent a similar one). I think
also since it requires the socket to be SOCK_STREAM, there can be only
one peer connected so it should be ok?

Tycho

> >  		return -1;
> >  
> >  	if (rst_file_params(fd, ui->ue->fown, ui->ue->flags))
> > @@ -1021,6 +1028,7 @@ static int collect_one_unixsk(void *o, ProtobufCMessage *base)
> >  		ui->name = NULL;
> >  
> >  	futex_init(&ui->prepared);
> > +	ui->queuer = 0;
> >  	ui->peer = NULL;
> >  	ui->flags = 0;
> >  	pr_info(" `- Got %#x peer %#x (name %s)\n",
> > @@ -1063,6 +1071,8 @@ int resolve_unix_peers(void)
> >  		}
> >  
> >  		ui->peer = peer;
> > +		if (!ui->queuer)
> > +			ui->queuer = ui->ue->ino;
> >  		if (ui == peer)
> >  			/* socket connected to self %) */
> >  			continue;
> > 
>