[lustre-devel] [PATCH 02/21] lustre: obd_class: remove csi_barrier from struct cl_sync_io

[NeilBrown <neilb@suse.com>]

On Mon, Feb 11 2019, James Simmons wrote:

>> This flag is used to ensure that structure isn't freed before
>> the wakeup completes.  The same can be achieved using the
>> csi_waitq.lock and calling wake_up_all_locked().
>>
>
> Reviewed-by: James Simmons <jsimmons@infradead.org>
>
>> Signed-off-by: NeilBrown <neilb@suse.com>
>> ---
>>  drivers/staging/lustre/lustre/include/cl_object.h |    2 --
>>  drivers/staging/lustre/lustre/obdclass/cl_io.c    |   16 +++++++---------
>>  2 files changed, 7 insertions(+), 11 deletions(-)
>> 
>> diff --git a/drivers/staging/lustre/lustre/include/cl_object.h b/drivers/staging/lustre/lustre/include/cl_object.h
>> index 71ba73cdbb5e..13d79810dd39 100644
>> --- a/drivers/staging/lustre/lustre/include/cl_object.h
>> +++ b/drivers/staging/lustre/lustre/include/cl_object.h
>> @@ -2391,8 +2391,6 @@ struct cl_sync_io {
>>  	atomic_t		csi_sync_nr;
>>  	/** error code. */
>>  	int			csi_sync_rc;
>> -	/** barrier of destroy this structure */
>> -	atomic_t		csi_barrier;
>>  	/** completion to be signaled when transfer is complete. */
>>  	wait_queue_head_t	csi_waitq;
>>  };
>> diff --git a/drivers/staging/lustre/lustre/obdclass/cl_io.c b/drivers/staging/lustre/lustre/obdclass/cl_io.c
>> index e9ad055f84b8..beac7e8bc92a 100644
>> --- a/drivers/staging/lustre/lustre/obdclass/cl_io.c
>> +++ b/drivers/staging/lustre/lustre/obdclass/cl_io.c
>> @@ -1047,7 +1047,6 @@ void cl_sync_io_init(struct cl_sync_io *anchor, int nr)
>>  	memset(anchor, 0, sizeof(*anchor));
>>  	init_waitqueue_head(&anchor->csi_waitq);
>>  	atomic_set(&anchor->csi_sync_nr, nr);
>> -	atomic_set(&anchor->csi_barrier, nr > 0);
>>  	anchor->csi_sync_rc = 0;
>>  }
>>  EXPORT_SYMBOL(cl_sync_io_init);
>> @@ -1080,11 +1079,10 @@ int cl_sync_io_wait(const struct lu_env *env, struct cl_sync_io *anchor,
>>  	} else {
>>  		rc = anchor->csi_sync_rc;
>>  	}
>> +	/* We take the lock to ensure that cl_sync_io_note() has finished */
>> +	spin_lock(&anchor->csi_waitq.lock);
>
> I don't think I every seen any use the internal lock for the wait_queue
> in such a method. Most creative approach.

You need to get more :-)

There is a macro
   wait_event_interruptible_locked()
which explicitly supports this model.  Only used 4 times in the kernel
so not very popular yet.
The various forms of wake_up_locked are used a bit more often.
I don't remember where I first saw it.
It is a neat idea!

Thanks,
NeilBrown



>
>>  	LASSERT(atomic_read(&anchor->csi_sync_nr) == 0);
>> -
>> -	/* wait until cl_sync_io_note() has done wakeup */
>> -	while (unlikely(atomic_read(&anchor->csi_barrier) != 0))
>> -		cpu_relax();
>> +	spin_unlock(&anchor->csi_waitq.lock);
>>  
>>  	return rc;
>>  }
>> @@ -1104,11 +1102,11 @@ void cl_sync_io_note(const struct lu_env *env, struct cl_sync_io *anchor,
>>  	 * IO.
>>  	 */
>>  	LASSERT(atomic_read(&anchor->csi_sync_nr) > 0);
>> -	if (atomic_dec_and_test(&anchor->csi_sync_nr)) {
>> +	if (atomic_dec_and_lock(&anchor->csi_sync_nr,
>> +				&anchor->csi_waitq.lock)) {
>>  
>> -		wake_up_all(&anchor->csi_waitq);
>> -		/* it's safe to nuke or reuse anchor now */
>> -		atomic_set(&anchor->csi_barrier, 0);
>> +		wake_up_all_locked(&anchor->csi_waitq);
>> +		spin_unlock(&anchor->csi_waitq.lock);
>>  
>>  		/* Can't access anchor any more */
>>  	}
>> 
>> 
>> 
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