linux-kernel - Re: [PATCH] zfcp: add some internal zfcp adapter statistics

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Message-Id: <200711051612.44273.swen@vnet.ibm.com>
Date:	Mon, 5 Nov 2007 16:12:43 +0100
From:	Swen Schillig <swen@...t.ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	James Bottomley <James.Bottomley@...eleye.com>,
	Christof Schmitt <christof.schmitt@...ibm.com>,
	linux-scsi@...r.kernel.org,
	Linux on 390 Port <LINUX-390@...marist.edu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zfcp: add some internal zfcp adapter statistics

On Saturday 03 November 2007 10:17, Heiko Carstens wrote:
> > +static void zfcp_fsf_req_latency(struct zfcp_fsf_req *fsf_req)
> > +{
> > +	struct fsf_qual_latency_info *lat_inf;
> > +	struct zfcp_unit *unit;
> > +
> > +	lat_inf = &fsf_req->qtcb->prefix.prot_status_qual.latency_info;
> > +	unit = fsf_req->unit;
> > +
> > +	switch (fsf_req->qtcb->bottom.io.data_direction) {
> > +	case FSF_DATADIR_READ:
> > +		unit->latencies.read.channel += lat_inf->channel_lat;
> > +		unit->latencies.read.fabric += lat_inf->fabric_lat;
> > +		unit->latencies.read.counter++;
> > +		break;
> > +	case FSF_DATADIR_WRITE:
> > +		unit->latencies.write.channel += lat_inf->channel_lat;
> > +		unit->latencies.write.fabric += lat_inf->fabric_lat;
> > +		unit->latencies.write.counter++;
> > +		break;
> > +	case FSF_DATADIR_CMND:
> > +		unit->latencies.cmd.channel += lat_inf->channel_lat;
> > +		unit->latencies.cmd.fabric += lat_inf->fabric_lat;
> > +		unit->latencies.cmd.counter++;
> > +		break;
> > +	}
> > +}
> 
> These statistics are concurrently updated from several cpus without
> any locking. That looks like a bug.
> 
> > +zfcp_sysfs_unit_##_name##_latency_show(struct device *dev,		\
> > +				       struct device_attribute *attr,	\
> > +				       char *buf) {			\
> > +	struct scsi_device *sdev = to_scsi_device(dev);			\
> > +	struct zfcp_unit *unit = sdev->hostdata;			\
> > +	struct zfcp_latencies *lat = &unit->latencies;			\
> > +	struct zfcp_adapter *adapter = unit->port->adapter;		\
> > +									\
> > +	return sprintf(buf, "%u %u %u\n",				\
> > +		       lat->_name.fabric * adapter->timer_ticks / 1000, \
> > +		       lat->_name.channel * adapter->timer_ticks / 1000,\
> > +		       lat->_name.counter);				\
> 
> In addition they can be read concurrently from userspace without any
> locking... Since you put several values together in the output I assume
> this is supposed to be some sort of snapshot, which it currently isn't.
> 
> > +static int
> > +zfcp_sysfs_adapter_ex_config(struct class_device *cdev,
> > +			     struct fsf_qtcb_bottom_config **qtcb_config)
> > +{
> > +	struct Scsi_Host *scsi_host = class_to_shost(cdev);
> > +	struct zfcp_adapter *adapter = (struct zfcp_adapter *)
> > +						scsi_host->hostdata[0];
> > +
> > +	if (!(adapter->adapter_features & FSF_FEATURE_MEASUREMENT_DATA)) {
> > +		ZFCP_LOG_NORMAL("error: Enhanced measurement feature not "
> > +				"supported");
> > +		return -EOPNOTSUPP;
> > +	}
> > +
> > +	*qtcb_config = kzalloc(sizeof(struct fsf_qtcb_bottom_config),
> > +			       GFP_KERNEL);
> > +	if (!*qtcb_config)
> > +		return -ENOMEM;
> > +
> > +	return zfcp_fsf_exchange_config_data_sync(adapter, *qtcb_config);
> > +}
> > +
> > +static ssize_t
> > +zfcp_sysfs_adapter_request_show(struct class_device *cdev, char *buf)
> > +{
> > +	struct fsf_qtcb_bottom_config *qtcb_config;
> > +	int retval;
> > +
> > +	retval = zfcp_sysfs_adapter_ex_config(cdev, &qtcb_config);
> > +
> > +	if (!retval)
> > +		retval = sprintf(buf, "%lu %lu %lu\n",
> > +				 qtcb_config->stat_info.input_req,
> > +				 qtcb_config->stat_info.output_req,
> > +				 qtcb_config->stat_info.control_req);
> > +
> > +	kfree(qtcb_config);
> > +	return retval;
> > +}
> 
> You're going to call kfree with some random value if the adapter doesn't
> support the measurement data feature.
> 
Ok, valid points. 
I changed the patch to meet the above described issues.
Before I will post the modified version I want to do some testing (and an internal review).

The updated version will follow soon (hopefully this week), thanks for reviewing.

Cheers Swen
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