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[SCSI] ibmvfc: Fix command completion handling

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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@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
This commit is contained in:
Brian King 2010-04-20 14:21:33 -05:00 committed by James Bottomley
parent 859e816704
commit f5832fa2f8
1 changed files with 6 additions and 0 deletions
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6
drivers/scsi/ibmvscsi/ibmvfc.c
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@ -3013,6 +3013,7 @@ static struct ibmvfc_async_crq *ibmvfc_next_async_crq(struct ibmvfc_host *vhost)
if (crq->valid & 0x80) {
if (++async_crq->cur == async_crq->size)
async_crq->cur = 0;
rmb();
} else
crq = NULL;
@ -3035,6 +3036,7 @@ static struct ibmvfc_crq *ibmvfc_next_crq(struct ibmvfc_host *vhost)
if (crq->valid & 0x80) {
if (++queue->cur == queue->size)
queue->cur = 0;
rmb();
} else
crq = NULL;
@ -3083,12 +3085,14 @@ 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);
@ -3096,10 +3100,12 @@ 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;
}