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

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

15.11.2012 01:01, J. Bruce Fields пишет:
> On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
>> 07.11.2012 22:33, J. Bruce Fields пишет:
>>> 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