Re: [PATCH] quiet down swiotlb warnings

Rik van Riel
2007-06-01T18:19:16Z

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Christoph Hellwig wrote:
> On Fri, Jun 01, 2007 at 09:01:45PM +0200, Andi Kleen wrote:
>> Bad idea imho. swiotlb mappings should always lead to printk by default
>> because it is pretty dangerous.
>>
>> One possible solution for this I could think of would be to define a
>> new pci_map_sg_couldfail() or similar that doesn't warn and use a weak
>> fallback just calling pci_map_sg on other IOMMU implementations.
>
> pci_map_sg is defined to be failing when running out of ressources, which
> is perfectly fine. We don't printk on kmalloc failures either (actually
> in some cases which is highly annoying and leads people to stick a
> __GFP_NOWARN into various places)

Andi, I could see your "pretty dangerous" case applying
when do_panic is set, but not in any other circumstances.

Does the patch below look better to you?

Signed-off-by: Rik van Riel <riel@redhat.com>

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--- linux-2.6.21.noarch/lib/swiotlb.c.quiet 2007-06-01 13:23:04.000000000 -0400
+++ linux-2.6.21.noarch/lib/swiotlb.c 2007-06-01 14:18:26.000000000 -0400
@@ -505,6 +505,7 @@ swiotlb_free_coherent(struct device *hwd
static void
swiotlb_full(struct device *dev, size_t size, int dir, int do_panic)
{
+ static int warnings = 0;
/*
* Ran out of IOMMU space for this operation. This is very bad.
* Unfortunately the drivers cannot handle this operation properly.
@@ -512,8 +513,9 @@ swiotlb_full(struct device *dev, size_t
* When the mapping is small enough return a static buffer to limit
* the damage, or panic when the transfer is too big.
*/
- printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
- "device %s\n", size, dev ? dev->bus_id : "?");
+ if (do_panic || ++warnings < 5)
+ printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
+ "device %s\n", size, dev ? dev->bus_id : "?");

if (size > io_tlb_overflow && do_panic) {
if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)