dma-debug: change hash_bucket_find from first-fit to best-fit (7caf6a49) · Commits · 戴 / test

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>

lib/dma-debug.c

+39 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}

		/*

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