linux-kernel - Re: [PATCH UPDATED 38/40] cifs: use workqueue instead of slow-work

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Date:	Sun, 24 Jan 2010 07:13:34 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	torvalds@...ux-foundation.org, mingo@...e.hu, peterz@...radead.org,
	awalls@...ix.net, linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org,
	Steve French <sfrench@...ba.org>
Subject: Re: [PATCH UPDATED 38/40] cifs: use workqueue instead of slow-work

On Sun, 24 Jan 2010 17:25:18 +0900
Tejun Heo <tj@...nel.org> wrote:

> Hello,
> 
> On 01/22/2010 08:45 PM, Jeff Layton wrote:
> >> @@ -584,13 +583,18 @@ is_valid_oplock_break(struct smb_hdr *bu
> >>  				pCifsInode->clientCanCacheAll = false;
> >>  				if (pSMB->OplockLevel == 0)
> >>  					pCifsInode->clientCanCacheRead = false;
> >> -				rc = slow_work_enqueue(&netfile->oplock_break);
> >> -				if (rc) {
> >> -					cERROR(1, ("failed to enqueue oplock "
> >> -						   "break: %d\n", rc));
> >> -				} else {
> >> -					netfile->oplock_break_cancelled = false;
> >> -				}
> >> +
> >> +				/*
> >> +				 * cifs_oplock_break_put() can't be called
> >> +				 * from here.  Get reference after queueing
> >> +				 * succeeded.  cifs_oplock_break() will
> >> +				 * synchronize using GlobalSMSSeslock.
> >> +				 */
> >> +				if (queue_work(system_single_wq,
> >> +					       &netfile->oplock_break))
> >> +					cifs_oplock_break_get(netfile);
> >> +				netfile->oplock_break_cancelled = false;
> >> +
> > 
> > I think we want to move the setting of netfile->oplock_break_cancelled
> > inside of the if above it.
> > 
> > If the work is already queued, I don't think we want to set the flag to
> > false. Doing so might be problematic if we somehow end up processing
> > this oplock break after a previous oplock break/reconnect/reopen
> > sequence, but while the initial oplock break is still running.
> 
> Hmmm.... I can surely do that but that would be different from the
> original code.  slow_work_enqueue() doesn't distinguish between
> successful enqueue and the one which got ignored because the work was
> already queued.  With conversion to queue_work(), there's no failure
> case there so setting oplock_break_cancelled always is equivalent to
> the original code.  Even if changing it is the right thing to do, it
> should probably be done with a separate patch as it changes the logic.
> Are you sure it needs to be changed?
> 

I'm pretty sure we do. This flag only gets set to true if there's a
reconnection event. If there is one, then any oplock break queued up
before that happened is now invalid and shouldn't be sent.

It's a fairly minor point however. Even if we send the oplock break,
it's very unlikely to be treated as valid by the server as I don't
think the file would have a chance to be reopened prior to that.

If this is the way that the code works now, then let's go ahead with
your version and I'll plan to queue up a separate patch to change that
behavior after your changes go in.

Thanks,
-- 
Jeff Layton <jlayton@...hat.com>
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