[lxc-devel] [PATCH] add process_lock()/unlock() in save_config()

[Serge Hallyn]

Quoting Dwight Engen (dwight.engen at oracle.com):
> On Tue, 12 Nov 2013 14:42:54 -0600
> Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> 
> > Quoting Dwight Engen (dwight.engen at oracle.com):
> > > This is likely unnecessary, but is consistent with other uses of
> > > fopen()/fclose() in lxc.
> > > 
> > > Signed-off-by: Dwight Engen <dwight.engen at oracle.com>
> > 
> > Do you think, regardless of your other fix, that it would still be
> > worth adding an fsync?
> 
> Hmm, good question. I guess its possible lxcapi_save_config() could be
> called by two different user processes for the same container and we'd

They'd be protected by container_mem_lock(), but I think you've shown
that's not enough.

Which might mean that what we need is to always fsync c->configfile
at end of container_mem_lock()...

> wind up with a similar situation. Seems like we're trying to use the
> disk lock to protect against that, but it wasn't enough so maybe we do
> need the fflush and fsync in there too. I think I'd have to write a
> test to show the corruption and also then that the fflush and fsync
> fixes it like it did for the create() flow to convince myself :)
> 
> > 
> > Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>
> > 
> > > ---
> > >  src/lxc/lxccontainer.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> > > index ede0113..c7b2f5e 100644
> > > --- a/src/lxc/lxccontainer.c
> > > +++ b/src/lxc/lxccontainer.c
> > > @@ -1696,11 +1696,15 @@ static bool lxcapi_save_config(struct
> > > lxc_container *c, const char *alt_file) if (lret)
> > >  		return false;
> > >  
> > > +	process_lock();
> > >  	fout = fopen(alt_file, "w");
> > > +	process_unlock();
> > >  	if (!fout)
> > >  		goto out;
> > >  	write_config(fout, c->lxc_conf);
> > > +	process_lock();
> > >  	fclose(fout);
> > > +	process_unlock();
> > >  	ret = true;
> > >  
> > >  out:
> > > -- 
> > > 1.8.3.1
> > > 
> > > 
> > > ------------------------------------------------------------------------------
> > > DreamFactory - Open Source REST & JSON Services for HTML5 & Native
> > > Apps OAuth, Users, Roles, SQL, NoSQL, BLOB Storage and External API
> > > Access Free app hosting. Or install the open source package on any
> > > LAMP server. Sign up and see examples for AngularJS, jQuery, Sencha
> > > Touch and Native!
> > > http://pubads.g.doubleclick.net/gampad/clk?id=63469471&iu=/4140/ostg.clktrk
> > > _______________________________________________ Lxc-devel mailing
> > > list Lxc-devel at lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/lxc-devel
>