Re: [PATCH] dma-debug: hash_bucket_find needs to allow for offsetswithin an entry

From: Roedel, Joerg
Date: Wed Jul 20 2011 - 06:38:25 EST


Hi Neil,

thanks for your work on this :)

On Tue, Jul 19, 2011 at 01:41:18PM -0400, Neil Horman wrote:
> lib/dma-debug.c | 17 +++++++++++++++--
> 1 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> index db07bfd..333f0ee 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -248,10 +248,23 @@ static struct dma_debug_entry *hash_bucket_find(struct hash_bucket *bucket,
> {
> struct dma_debug_entry *entry, *ret = NULL;
> int matches = 0, match_lvl, last_lvl = 0;
> + u64 estart, eend, rstart, rend;
> +
> + rstart = ref->dev_addr;
> + rend = rstart + ref->size;
>
> list_for_each_entry(entry, &bucket->list, list) {
> - if ((entry->dev_addr != ref->dev_addr) ||
> - (entry->dev != ref->dev))
> + estart = entry->dev_addr;
> + eend = estart + entry->size;
> +
> + /*
> + * An entry matches if the address range specified by the ref
> + * dev_addr and size falls entirely within the range specified
> + * by the entries dev_addr and size and the devices match
> + */
> + if (entry->dev != ref->dev)
> + continue;
> + if ((estart > rstart) || (eend < rend))
> continue;
>
> /*

But it is not that easy. The hash_fn works on the dev_addr, this means
to search all entries which might match you need to scan multiple
hash-buckets potentially.
In fact, you need to scan

hash_fn(estart) <= idx <= hash_fn(eend)

to be sure. The patch above also lifts up the check_unmap which is not
desired.

Thanks,

Joerg

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