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SubjectRe: [PATCH] aic94xx: Don't call pci_map_sg for already-mapped scatterlists
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On Fri, 2006-11-10 at 16:59 -0800, Darrick J. Wong wrote:
> It turns out that libata has already dma_map_sg'd the scatterlist
> entries that go with an ata_queued_cmd by the time it calls
> sas_ata_qc_issue. sas_ata_qc_issue passes this scatterlist to aic94xx.
> Unfortunately, aic94xx assumes that any scatterlist passed to it needs
> to be pci_map_sg'd... which blows away the mapping that libata created!
> This causes (on a x260) Calgary IOMMU table leaks and duplicate frees
> when aic94xx and libata try to {pci,dma}_unmap_sg the scatterlist.
>
> Since dma_map_sg and pci_map_sg are fed the same struct device, I think
> it's safe to add a flag to sas_task that tells aic94xx that it need
> not map the scatterlist. It didn't break anything on the x260, though
> I don't have any SATAPI devices to test with. Is this the correct
> approach to fixing this problem?

Rather than introduce an extra flag, I think we can key of the protocol
flag: libata is the only thing that initiates STP tasks. How does this
look?

James

Index: BUILD-2.6/drivers/scsi/aic94xx/aic94xx_task.c
===================================================================
--- BUILD-2.6.orig/drivers/scsi/aic94xx/aic94xx_task.c 2006-12-03 17:57:27.000000000 -0600
+++ BUILD-2.6/drivers/scsi/aic94xx/aic94xx_task.c 2006-12-05 10:43:01.000000000 -0600
@@ -74,8 +74,13 @@ static inline int asd_map_scatterlist(st
return 0;
}

- num_sg = pci_map_sg(asd_ha->pcidev, task->scatter, task->num_scatter,
- task->data_dir);
+ /* STP tasks come from libata which has already mapped
+ * the SG list */
+ if (task->task_proto == SAS_PROTOCOL_STP)
+ num_sg = task->num_scatter;
+ else
+ num_sg = pci_map_sg(asd_ha->pcidev, task->scatter,
+ task->num_scatter, task->data_dir);
if (num_sg == 0)
return -ENOMEM;

@@ -120,8 +125,9 @@ static inline int asd_map_scatterlist(st

return 0;
err_unmap:
- pci_unmap_sg(asd_ha->pcidev, task->scatter, task->num_scatter,
- task->data_dir);
+ if (task->task_proto != SAS_PROTOCOL_STP)
+ pci_unmap_sg(asd_ha->pcidev, task->scatter, task->num_scatter,
+ task->data_dir);
return res;
}

@@ -142,8 +148,9 @@ static inline void asd_unmap_scatterlist
}

asd_free_coherent(asd_ha, ascb->sg_arr);
- pci_unmap_sg(asd_ha->pcidev, task->scatter, task->num_scatter,
- task->data_dir);
+ if (task->task_proto != SAS_PROTOCOL_STP)
+ pci_unmap_sg(asd_ha->pcidev, task->scatter, task->num_scatter,
+ task->data_dir);
}

/* ---------- Task complete tasklet ---------- */

-
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