Commands which are completed by the VIOS are placed on a CRQ
in kernel memory for the ibmvfc driver to process. Each CRQ
entry is 16 bytes. The ibmvfc driver reads the first 8 bytes
to check if the entry is valid, then reads the next 8 bytes to get
the handle, which is a pointer the completed command. This fixes
an issue seen on Power 7 where the processor reordered the
loads from memory, resulting in processing command completion
with a stale handle. This could result in command timeouts,
and also early completion of commands.
Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx>
---
drivers/scsi/ibmvscsi/ibmvfc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN drivers/scsi/ibmvscsi/ibmvfc.c~ibmvfc_barrier drivers/scsi/ibmvscsi/ibmvfc.c
--- linux-2.6/drivers/scsi/ibmvscsi/ibmvfc.c~ibmvfc_barrier 2010-04-20 08:47:48.000000000 -0500
+++ linux-2.6-bjking1/drivers/scsi/ibmvscsi/ibmvfc.c 2010-04-20 08:47:48.000000000 -0500
@@ -3012,6 +3012,7 @@ static struct ibmvfc_async_crq *ibmvfc_n
if (crq->valid & 0x80) {
if (++async_crq->cur == async_crq->size)
async_crq->cur = 0;
+ rmb();
} else
crq = NULL;
@@ -3034,6 +3035,7 @@ static struct ibmvfc_crq *ibmvfc_next_cr
if (crq->valid & 0x80) {
if (++queue->cur == queue->size)
queue->cur = 0;
+ rmb();
} else
crq = NULL;
@@ -3082,12 +3084,14 @@ static void ibmvfc_tasklet(void *data)
while ((async = ibmvfc_next_async_crq(vhost)) != NULL) {
ibmvfc_handle_async(async, vhost);
async->valid = 0;
+ wmb();
}
/* Pull all the valid messages off the CRQ */
while ((crq = ibmvfc_next_crq(vhost)) != NULL) {
ibmvfc_handle_crq(crq, vhost);
crq->valid = 0;
+ wmb();
}
vio_enable_interrupts(vdev);
@@ -3095,10 +3099,12 @@ static void ibmvfc_tasklet(void *data)
vio_disable_interrupts(vdev);
ibmvfc_handle_async(async, vhost);
async->valid = 0;
+ wmb();
} else if ((crq = ibmvfc_next_crq(vhost)) != NULL) {
vio_disable_interrupts(vdev);
ibmvfc_handle_crq(crq, vhost);
crq->valid = 0;
+ wmb();
} else
done = 1;
}
_
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
