linux-kernel - Re: [PATCH] lib/dma-debug: fix bucket_find

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Message-Id: <20150319150901.a004c3dc15a49a1859e467ff@linux-foundation.org>
Date:	Thu, 19 Mar 2015 15:09:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Florian Fainelli <f.fainelli@...il.com>,
	Horia Geanta <horia.geanta@...escale.com>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH] lib/dma-debug: fix bucket_find_contain

On Mon, 16 Mar 2015 19:24:29 +0100 (CET) Sebastian Ott <sebott@...ux.vnet.ibm.com> wrote:

> bucket_find_contain will search the bucket list for a dma_debug_entry. When
> the entry isn't found it needs to search other buckets too, since only the
> start address of a dma range is hashed (which might be in a different bucket).
> 
> A copy of the dma_debug_entry is used to get the previous hash bucket but when
> its list is searched the original dma_debug_entry is to be used not its
> modified copy.
> 
> This fixes false "device driver tries to sync DMA memory it has not allocated"
> warnings.

The changelog doesn't help me understand how serious this is.  A 4.0
thing?  -stable?

> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -361,7 +361,7 @@ static struct dma_debug_entry *bucket_fi
>  	unsigned int range = 0;
>  
>  	while (range <= max_range) {
> -		entry = __hash_bucket_find(*bucket, &index, containing_match);
> +		entry = __hash_bucket_find(*bucket, ref, containing_match);
>  
>  		if (entry)
>  			return entry;

This code just got more confusing :(  Are you sure we aren't supposed to
use `ref' in bucket_find_contain()'s call to get_hash_bucket()?

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