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scsi: fix the {host,target,device}_blocked counter mess

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Seems like these counters are missing any sort of synchronization for
updates, as a over 10 year old comment from me noted.  Fix this by
using atomic counters, and while we're at it also make sure they are
in the same cacheline as the _busy counters and not needlessly stored
to in every I/O completion.

With the new model the _busy counters can temporarily go negative,
so all the readers are updated to check for > 0 values.  Longer
term every successful I/O completion will reset the counters to zero,
so the temporarily negative values will not cause any harm.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
This commit is contained in:
Christoph Hellwig
2014-01-23 12:07:41 +01:00
parent 71e75c97f9
commit cd9070c9c5
5 changed files with 58 additions and 53 deletions
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10
drivers/scsi/scsi_sysfs.c
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@@ -584,7 +584,6 @@ static int scsi_sdev_check_buf_bit(const char *buf)
/*
* Create the actual show/store functions and data structures.
*/
sdev_rd_attr (device_blocked, "%d\n");
sdev_rd_attr (type, "%d\n");
sdev_rd_attr (scsi_level, "%d\n");
sdev_rd_attr (vendor, "%.8s\n");
@@ -600,6 +599,15 @@ sdev_show_device_busy(struct device *dev, struct device_attribute *attr,
}
static DEVICE_ATTR(device_busy, S_IRUGO, sdev_show_device_busy, NULL);
static ssize_t
sdev_show_device_blocked(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct scsi_device *sdev = to_scsi_device(dev);
return snprintf(buf, 20, "%d\n", atomic_read(&sdev->device_blocked));
}
static DEVICE_ATTR(device_blocked, S_IRUGO, sdev_show_device_blocked, NULL);
/*
* TODO: can we make these symlinks to the block layer ones?
*/