linux-kernel - Re: [PATCH,resend] Fix strange panic message selection logic when swiotlb fills up

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Date:	Thu, 20 Aug 2009 16:25:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Casey Dahlin <cdahlin@...hat.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	beckyb@...nel.crashing.org
Subject: Re: [PATCH,resend] Fix strange panic message selection logic when
 swiotlb fills up

On Thu, 20 Aug 2009 15:52:28 -0400
Casey Dahlin <cdahlin@...hat.com> wrote:

> swiotlb_full in lib/swiotlb.c throws one of two panic messages based on whether
> the direction of transfer is from the device or to the device. The logic around
> this is somewhat weird in the case of bidirectional transfers. It appears to
> want to throw both in succession, but since its a panic only the first makes it.
> 
> This patch adds a third, separate error for DMA_BIDIRECTIONAL to make things a
> bit clearer.
> 
> Signed-off-by: Casey Dahlin <cdahlin@...hat.com>
> 
> ---
>  lib/swiotlb.c |   15 +++++++++------
>  1 files changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index bffe6d7..35e01b3 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -625,12 +625,15 @@ swiotlb_full(struct device *dev, size_t size, int dir, int do_panic)
>  	printk(KERN_ERR "DMA: Out of SW-IOMMU space for %zu bytes at "
>  	       "device %s\n", size, dev ? dev_name(dev) : "?");
>  
> -	if (size > io_tlb_overflow && do_panic) {
> -		if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
> -			panic("DMA: Memory would be corrupted\n");
> -		if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
> -			panic("DMA: Random memory would be DMAed\n");
> -	}
> +	if (size <= io_tlb_overflow || !do_panic)
> +		return;
> +
> +	if (dir == DMA_BIDIRECTIONAL)
> +		panic("DMA: Random memory could be corrupted or DMAed\n");
> +	if (dir == DMA_FROM_DEVICE)
> +		panic("DMA: Memory would be corrupted\n");
> +	if (dir == DMA_TO_DEVICE)
> +		panic("DMA: Random memory would be DMAed\n");
>  }
>  

Seems sane to me.

While we're there, how about we make the final message less ambiguous? 

--- a/lib/swiotlb.c~lib-swiotlbc-fix-strange-panic-message-selection-logic-when-swiotlb-fills-up-fix
+++ a/lib/swiotlb.c
@@ -633,7 +633,7 @@ swiotlb_full(struct device *dev, size_t 
 	if (dir == DMA_FROM_DEVICE)
 		panic("DMA: Memory would be corrupted\n");
 	if (dir == DMA_TO_DEVICE)
-		panic("DMA: Random memory would be DMAed\n");
+		panic("DMA: Random memory would be DMAed from\n");
 }
 
 /*
_

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