Re: [PATCH v3] SUNRPC: set desired file system root before connectinglocal transports

[Stanislav Kinsbursky]

15.11.2012 01:01, J. Bruce Fields ÐÐÑÐÑ:
> On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> > 07.11.2012 22:33, J. Bruce Fields ÐÐÑÐÑ:
> > > On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> > > > On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > > > > On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > > > > > So you're worried that a bug in the nfs code could modify the root and
> > > > > > then not restore it?
> > > > >
> > > > > At least the link you pointed to earlier never sets it back.
> > > >
> > > > This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> > > >
> > > > 	+	get_fs_root(current->fs, &root);
> > > > 	+	set_fs_root(current->fs, &transport->root);
> > > > 	+
> > > > 	 	status = xs_local_finish_connecting(xprt, sock);
> > > > 	+
> > > > 	+	set_fs_root(current->fs, &root);
> > > > 	+	path_put(&root);
> > > >
> > > > > Instead
> > > > > of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > > > > and not care about current->fs->root at all.
> > > >
> > > > The annoyance is that the lookup happens somewhere lower down in the
> > > > networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> > > > need some new (internal) API.  We'd likely be the only user of that new
> > > > API.
> > >
> > > So, if the only drawback is really just the risk of introducing a bug
> > > that leaves the fs_root changed--the above seems simple enough for that
> > > not to be a great risk, right?
> >
> > If we unshare rpciod fs struct (which is exported already), then we
>
> I'm not sure what you mean by that.  Do workqueues actually have their
> own dedicated set of associated tasks?  I thought all workqueues shared
> a common pool of tasks these days.

Any kernel thread is cloned in kthreadd context with CLONE_FS flag.
I.e. all of them shares same fs struct, and changing fs->root in one of kthreads 
will affect all others.
That's why either fs struct have to be unshared to swap fs->root or fs->cwd, or 
the whole fs struct have to swapped.


--
Best regards,
Stanislav Kinsbursky
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