[lxc-devel] [PATCH] RFC: commands: handle epipe

[Serge Hallyn]

Quoting Stéphane Graber (stgraber at ubuntu.com):
> On Tue, Mar 25, 2014 at 05:58:32PM -0400, Dwight Engen wrote:
> > On Tue, 25 Mar 2014 15:50:06 -0500
> > Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> > 
> > > If we start a lxc_wait on a container while it is exiting, it is
> > > possible that we open the command socket, then the monitor closes
> > > all its mainloop sockets and exit, then we send our credentials.
> > > Then we get killed by SIGPIPE.
> > 
> > Hey Serge, this is an interesting condition. I'm a bit confused where
> > the race is, looking at lxc_wait it looks like we get the monitor open
> > before opening the command socket with lxc_getstate, and the monitor
> > shouldn't exit while we are still a client of it.
> 
> It's a race which has been causing dozens of testrun failures on the CI
> infrastructure, so it's reasonably easy to hit :)
> 
> And I think Serge meant s/monitor/command/ in there, the SIGPIPE we were
> getting was from the command socket when the container was about to die
> and exit.

Yeah, unfortunately I call the task which waits on the container init
the 'container monitor'.  Suppose I need a better name for it...  But
that's what it does :)

> > > Handle that case, recognizing that if we get sigpipe then the
> > > container is (now) stopped.
> > 
> > This makes sense in general, so I agree with the change.
> >  
> > > Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> > > ---
> > >  src/lxc/af_unix.c  |  4 ++--
> > >  src/lxc/commands.c | 11 ++++++++++-
> > >  2 files changed, 12 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/src/lxc/af_unix.c b/src/lxc/af_unix.c
> > > index a2de73e..46d8e50 100644
> > > --- a/src/lxc/af_unix.c
> > > +++ b/src/lxc/af_unix.c
> > > @@ -158,7 +158,7 @@ int lxc_abstract_unix_send_fd(int fd, int sendfd,
> > > void *data, size_t size) msg.msg_iov = &iov;
> > >  	msg.msg_iovlen = 1;
> > >  
> > > -	return sendmsg(fd, &msg, 0);
> > > +	return sendmsg(fd, &msg, MSG_NOSIGNAL);
> > >  }
> > >  
> > >  int lxc_abstract_unix_recv_fd(int fd, int *recvfd, void *data,
> > > size_t size) @@ -230,7 +230,7 @@ int
> > > lxc_abstract_unix_send_credential(int fd, void *data, size_t size)
> > > msg.msg_iov = &iov; msg.msg_iovlen = 1;
> > >  
> > > -	return sendmsg(fd, &msg, 0);
> > > +	return sendmsg(fd, &msg, MSG_NOSIGNAL);
> > >  }
> > >  
> > >  int lxc_abstract_unix_rcv_credential(int fd, void *data, size_t size)
> > > diff --git a/src/lxc/commands.c b/src/lxc/commands.c
> > > index 6b46c2c..b71274c 100644
> > > --- a/src/lxc/commands.c
> > > +++ b/src/lxc/commands.c
> > > @@ -263,6 +263,8 @@ static int lxc_cmd(const char *name, struct
> > > lxc_cmd_rr *cmd, int *stopped, 
> > >  	ret = lxc_abstract_unix_send_credential(sock, &cmd->req,
> > > sizeof(cmd->req)); if (ret != sizeof(cmd->req)) {
> > > +		if (errno == EPIPE)
> > > +			goto epipe;
> > >  		SYSERROR("command %s failed to send req to '@%s' %d",
> > >  			 lxc_cmd_str(cmd->req.cmd), offset, ret);
> > >  		if (ret >=0)
> > > @@ -271,8 +273,10 @@ static int lxc_cmd(const char *name, struct
> > > lxc_cmd_rr *cmd, int *stopped, }
> > >  
> > >  	if (cmd->req.datalen > 0) {
> > > -		ret = send(sock, cmd->req.data, cmd->req.datalen, 0);
> > > +		ret = send(sock, cmd->req.data, cmd->req.datalen,
> > > MSG_NOSIGNAL); if (ret != cmd->req.datalen) {
> > > +			if (errno == EPIPE)
> > > +				goto epipe;
> > >  			SYSERROR("command %s failed to send request
> > > data to '@%s' %d", lxc_cmd_str(cmd->req.cmd), offset, ret);
> > >  			if (ret >=0)
> > > @@ -289,6 +293,11 @@ out:
> > >  		cmd->rsp.ret = sock;
> > >  
> > >  	return ret;
> > > +
> > > +epipe:
> > > +	close(sock);
> > > +	*stopped = 1;
> > > +	return 0;
> > >  }
> > >  
> > >  int lxc_try_cmd(const char *name, const char *lxcpath)
> > 
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
> 
> -- 
> Stéphane Graber
> Ubuntu developer
> http://www.ubuntu.com



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