Re: [PATCH] quiet down swiotlb warnings

[Rik van Riel <riel@redhat.com>]

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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)