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dma-debug: change hash_bucket_find from first-fit to best-fit 

Some device drivers map the same physical address multiple times to a
dma address. Without an IOMMU this results in the same dma address being
put into the dma-debug hash multiple times. With a first-fit match in
hash_bucket_find() this function may return the wrong dma_debug_entry.

This can result in false positive warnings. This patch fixes it by
changing the first-fit behavior of hash_bucket_find() into a best-fit
algorithm.

Reported-by: Torsten Kaiser <just.for.lkml@googlemail.com>
Reported-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: lethal@linux-sh.org
Cc: just.for.lkml@googlemail.com
Cc: hancockrwd@gmail.com
Cc: jens.axboe@oracle.com
Cc: bharrosh@panasas.com
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
LKML-Reference: <20090605104132.GE24836@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Joerg Roedel 2009-06-05 12:01:35 +02:00 committed by Ingo Molnar
parent fe2245c905
commit 7caf6a49bb
1 changed files with 39 additions and 4 deletions
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43
lib/dma-debug.c
View File

@ -186,15 +186,50 @@ static void put_hash_bucket(struct hash_bucket *bucket,
static struct dma_debug_entry *hash_bucket_find(struct hash_bucket *bucket,
struct dma_debug_entry *ref)
{
struct dma_debug_entry *entry;
struct dma_debug_entry *entry, *ret = NULL;
int matches = 0, match_lvl, last_lvl = 0;
list_for_each_entry(entry, &bucket->list, list) {
if ((entry->dev_addr == ref->dev_addr) &&
(entry->dev == ref->dev))
if ((entry->dev_addr != ref->dev_addr) ||
(entry->dev != ref->dev))
continue;
/*
* Some drivers map the same physical address multiple
* times. Without a hardware IOMMU this results in the
* same device addresses being put into the dma-debug
* hash multiple times too. This can result in false
* positives being reported. Therfore we implement a
* best-fit algorithm here which returns the entry from
* the hash which fits best to the reference value
* instead of the first-fit.
*/
matches += 1;
match_lvl = 0;
entry->size == ref->size ? ++match_lvl : match_lvl;
entry->type == ref->type ? ++match_lvl : match_lvl;
entry->direction == ref->direction ? ++match_lvl : match_lvl;
if (match_lvl == 3) {
/* perfect-fit - return the result */
return entry;
} else if (match_lvl > last_lvl) {
/*
* We found an entry that fits better then the
* previous one
*/
last_lvl = match_lvl;
ret = entry;
}
}
return NULL;
/*
* If we have multiple matches but no perfect-fit, just return
* NULL.
*/
ret = (matches == 1) ? ret : NULL;
return ret;
}
/*