lkml.org 
[lkml]   [2008]   [Apr]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: nfs: infinite loop in fcntl(F_SETLKW)
From
On Sun, Apr 13, 2008 at 10:28:08AM +0200, Miklos Szeredi wrote:
> > Apologies, that was indeed a behavioral change introduced in a commit
> > that claimed just to be shuffling code around.
>
> Another complaint about this series: using EINPROGRESS to signal
> asynchronous locking looks really fishy. How does the filesystem
> know, that the caller wants to do async locking?

The caller sets a fl_grant callback. But I guess the interesting
question is how the caller knows that the filesystem is really going to
return the results asynchronously:

> How do we make sure,
> that the filesystem (like fuse or 9p, which "blindly" return the error
> from the server) doesn't return EINPROGRESS even when it's _not_ doing
> an asynchronous lock?

Right, there's no safeguard there--if fuse returns EINPROGRESS, then
we'll wait for a grant callback that's not going to come. It should
time out, so that's not a total disaster, but still.

Anyway, I'm not sure what to do about that.

>
> I think it would have been much cleaner to have a completely separate
> interface for async locking, instead of trying to cram that into
> f_op->lock().

Maybe so. ->lock() had quite a bit crammed into it even before this.

> Would that be possible to fix now? Or at least make EINPROGRESS a
> kernel-internal error value (>512), to make it that it has a special
> meaning for the _kernel only_?

Perhaps so.

The behavior of lockd will still depend to some degree on the exact
error returned from the filesystem--e.g. if you return -EAGAIN from
->lock() without later calling ->fl_grant() it will cause some
unexpected delays. (Though again clients will eventually give up and
poll for the lock.)

--b.


\
 
 \ /
  Last update: 2008-04-14 19:23    [W:0.145 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site