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

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Date:	Sun, 24 Jan 2010 17:25:18 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Jeff Layton <jlayton@...hat.com>
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

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?

Thanks.

-- 
tejun
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