Commit 3b7a6418 authored by Dan Williams's avatar Dan Williams Committed by Linus Torvalds
Browse files

dma debug: account for cachelines and read-only mappings in overlap tracking 

While debug_dma_assert_idle() checks if a given *page* is actively
undergoing dma the valid granularity of a dma mapping is a *cacheline*.
Sander's testing shows that the warning message "DMA-API: exceeded 7
overlapping mappings of pfn..." is falsely triggering.  The test is
simply mapping multiple cachelines in a given page.

Ultimately we want overlap tracking to be valid as it is a real api
violation, so we need to track active mappings by cachelines.  Update
the active dma tracking to use the page-frame-relative cacheline of the
mapping as the key, and update debug_dma_assert_idle() to check for all
possible mapped cachelines for a given page.

However, the need to track active mappings is only relevant when the
dma-mapping is writable by the device.  In fact it is fairly standard
for read-only mappings to have hundreds or thousands of overlapping
mappings at once.  Limiting the overlap tracking to writable
(!DMA_TO_DEVICE) eliminates this class of false-positive overlap
reports.

Note, the radix gang lookup is sub-optimal.  It would be best if it
stopped fetching entries once the search passed a page boundary.
Nevertheless, this implementation does not perturb the original net_dma
failing case.  That is to say the extra overhead does not show up in
terms of making the failing case pass due to a timing change.

References:
  http://marc.info/?l=linux-netdev&m=139232263419315&w=2
  http://marc.info/?l=linux-netdev&m=139217088107122&w=2



Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Reported-by: default avatarSander Eikelenboom <linux@eikelenboom.it>
Reported-by: default avatarDave Jones <davej@redhat.com>
Tested-by: default avatarDave Jones <davej@redhat.com>
Tested-by: default avatarSander Eikelenboom <linux@eikelenboom.it>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Francois Romieu <romieu@fr.zoreil.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 668f9abb

lib/dma-debug.c

+85 −46
Original line number Diff line number Diff line
@@ -424,111 +424,134 @@ void debug_dma_dump_mappings(struct device *dev) 
EXPORT_SYMBOL(debug_dma_dump_mappings);



/*

 * For each page mapped (initial page in the case of

 * dma_alloc_coherent/dma_map_{single|page}, or each page in a

 * scatterlist) insert into this tree using the pfn as the key. At

 * For each mapping (initial cacheline in the case of

 * dma_alloc_coherent/dma_map_page, initial cacheline in each page of a

 * scatterlist, or the cacheline specified in dma_map_single) insert

 * into this tree using the cacheline as the key. At

 * dma_unmap_{single|sg|page} or dma_free_coherent delete the entry.  If

 * the pfn already exists at insertion time add a tag as a reference

 * the entry already exists at insertion time add a tag as a reference

 * count for the overlapping mappings.  For now, the overlap tracking

 * just ensures that 'unmaps' balance 'maps' before marking the pfn

 * idle, but we should also be flagging overlaps as an API violation.

 * just ensures that 'unmaps' balance 'maps' before marking the

 * cacheline idle, but we should also be flagging overlaps as an API

 * violation.

 *

 * Memory usage is mostly constrained by the maximum number of available

 * dma-debug entries in that we need a free dma_debug_entry before

 * inserting into the tree.  In the case of dma_map_{single|page} and

 * dma_alloc_coherent there is only one dma_debug_entry and one pfn to

 * track per event.  dma_map_sg(), on the other hand,

 * consumes a single dma_debug_entry, but inserts 'nents' entries into

 * the tree.

 * inserting into the tree.  In the case of dma_map_page and

 * dma_alloc_coherent there is only one dma_debug_entry and one

 * dma_active_cacheline entry to track per event.  dma_map_sg(), on the

 * other hand, consumes a single dma_debug_entry, but inserts 'nents'

 * entries into the tree.

 *

 * At any time debug_dma_assert_idle() can be called to trigger a

 * warning if the given page is in the active set.

 * warning if any cachelines in the given page are in the active set.

 */

static RADIX_TREE(dma_active_pfn, GFP_NOWAIT);

static RADIX_TREE(dma_active_cacheline, GFP_NOWAIT);

static DEFINE_SPINLOCK(radix_lock);

#define ACTIVE_PFN_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1)

#define ACTIVE_CACHELINE_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1)

#define CACHELINE_PER_PAGE_SHIFT (PAGE_SHIFT - L1_CACHE_SHIFT)

#define CACHELINES_PER_PAGE (1 << CACHELINE_PER_PAGE_SHIFT)



static int active_pfn_read_overlap(unsigned long pfn)

static phys_addr_t to_cacheline_number(struct dma_debug_entry *entry)

{

	return (entry->pfn << CACHELINE_PER_PAGE_SHIFT) +

		(entry->offset >> L1_CACHE_SHIFT);

}



static int active_cacheline_read_overlap(phys_addr_t cln)

{

	int overlap = 0, i;



	for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)

		if (radix_tree_tag_get(&dma_active_pfn, pfn, i))

		if (radix_tree_tag_get(&dma_active_cacheline, cln, i))

			overlap |= 1 << i;

	return overlap;

}



static int active_pfn_set_overlap(unsigned long pfn, int overlap)

static int active_cacheline_set_overlap(phys_addr_t cln, int overlap)

{

	int i;



	if (overlap > ACTIVE_PFN_MAX_OVERLAP || overlap < 0)

	if (overlap > ACTIVE_CACHELINE_MAX_OVERLAP || overlap < 0)

		return overlap;



	for (i = RADIX_TREE_MAX_TAGS - 1; i >= 0; i--)

		if (overlap & 1 << i)

			radix_tree_tag_set(&dma_active_pfn, pfn, i);

			radix_tree_tag_set(&dma_active_cacheline, cln, i);

		else

			radix_tree_tag_clear(&dma_active_pfn, pfn, i);

			radix_tree_tag_clear(&dma_active_cacheline, cln, i);



	return overlap;

}



static void active_pfn_inc_overlap(unsigned long pfn)

static void active_cacheline_inc_overlap(phys_addr_t cln)

{

	int overlap = active_pfn_read_overlap(pfn);

	int overlap = active_cacheline_read_overlap(cln);



	overlap = active_pfn_set_overlap(pfn, ++overlap);

	overlap = active_cacheline_set_overlap(cln, ++overlap);



	/* If we overflowed the overlap counter then we're potentially

	 * leaking dma-mappings.  Otherwise, if maps and unmaps are

	 * balanced then this overflow may cause false negatives in

	 * debug_dma_assert_idle() as the pfn may be marked idle

	 * debug_dma_assert_idle() as the cacheline may be marked idle

	 * prematurely.

	 */

	WARN_ONCE(overlap > ACTIVE_PFN_MAX_OVERLAP,

		  "DMA-API: exceeded %d overlapping mappings of pfn %lx\n",

		  ACTIVE_PFN_MAX_OVERLAP, pfn);

	WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,

		  "DMA-API: exceeded %d overlapping mappings of cacheline %pa\n",

		  ACTIVE_CACHELINE_MAX_OVERLAP, &cln);

}



static int active_pfn_dec_overlap(unsigned long pfn)

static int active_cacheline_dec_overlap(phys_addr_t cln)

{

	int overlap = active_pfn_read_overlap(pfn);

	int overlap = active_cacheline_read_overlap(cln);



	return active_pfn_set_overlap(pfn, --overlap);

	return active_cacheline_set_overlap(cln, --overlap);

}



static int active_pfn_insert(struct dma_debug_entry *entry)

static int active_cacheline_insert(struct dma_debug_entry *entry)

{

	phys_addr_t cln = to_cacheline_number(entry);

	unsigned long flags;

	int rc;



	/* If the device is not writing memory then we don't have any

	 * concerns about the cpu consuming stale data.  This mitigates

	 * legitimate usages of overlapping mappings.

	 */

	if (entry->direction == DMA_TO_DEVICE)

		return 0;



	spin_lock_irqsave(&radix_lock, flags);

	rc = radix_tree_insert(&dma_active_pfn, entry->pfn, entry);

	rc = radix_tree_insert(&dma_active_cacheline, cln, entry);

	if (rc == -EEXIST)

		active_pfn_inc_overlap(entry->pfn);

		active_cacheline_inc_overlap(cln);

	spin_unlock_irqrestore(&radix_lock, flags);



	return rc;

}



static void active_pfn_remove(struct dma_debug_entry *entry)

static void active_cacheline_remove(struct dma_debug_entry *entry)

{

	phys_addr_t cln = to_cacheline_number(entry);

	unsigned long flags;



	/* ...mirror the insert case */

	if (entry->direction == DMA_TO_DEVICE)

		return;



	spin_lock_irqsave(&radix_lock, flags);

	/* since we are counting overlaps the final put of the

	 * entry->pfn will occur when the overlap count is 0.

	 * active_pfn_dec_overlap() returns -1 in that case

	 * cacheline will occur when the overlap count is 0.

	 * active_cacheline_dec_overlap() returns -1 in that case

	 */

	if (active_pfn_dec_overlap(entry->pfn) < 0)

		radix_tree_delete(&dma_active_pfn, entry->pfn);

	if (active_cacheline_dec_overlap(cln) < 0)

		radix_tree_delete(&dma_active_cacheline, cln);

	spin_unlock_irqrestore(&radix_lock, flags);

}



/**

 * debug_dma_assert_idle() - assert that a page is not undergoing dma

 * @page: page to lookup in the dma_active_pfn tree

 * @page: page to lookup in the dma_active_cacheline tree

 *

 * Place a call to this routine in cases where the cpu touching the page

 * before the dma completes (page is dma_unmapped) will lead to data
@@ -536,22 +559,38 @@ static void active_pfn_remove(struct dma_debug_entry *entry) 
 */

void debug_dma_assert_idle(struct page *page)

{

	static struct dma_debug_entry *ents[CACHELINES_PER_PAGE];

	struct dma_debug_entry *entry = NULL;

	void **results = (void **) &ents;

	unsigned int nents, i;

	unsigned long flags;

	struct dma_debug_entry *entry;

	phys_addr_t cln;



	if (!page)

		return;



	cln = (phys_addr_t) page_to_pfn(page) << CACHELINE_PER_PAGE_SHIFT;

	spin_lock_irqsave(&radix_lock, flags);

	entry = radix_tree_lookup(&dma_active_pfn, page_to_pfn(page));

	nents = radix_tree_gang_lookup(&dma_active_cacheline, results, cln,

				       CACHELINES_PER_PAGE);

	for (i = 0; i < nents; i++) {

		phys_addr_t ent_cln = to_cacheline_number(ents[i]);



		if (ent_cln == cln) {

			entry = ents[i];

			break;

		} else if (ent_cln >= cln + CACHELINES_PER_PAGE)

			break;

	}

	spin_unlock_irqrestore(&radix_lock, flags);



	if (!entry)

		return;



	cln = to_cacheline_number(entry);

	err_printk(entry->dev, entry,

		   "DMA-API: cpu touching an active dma mapped page "

		   "[pfn=0x%lx]\n", entry->pfn);

		   "DMA-API: cpu touching an active dma mapped cacheline [cln=%pa]\n",

		   &cln);

}



/*
@@ -568,9 +607,9 @@ static void add_dma_entry(struct dma_debug_entry *entry) 
	hash_bucket_add(bucket, entry);

	put_hash_bucket(bucket, &flags);



	rc = active_pfn_insert(entry);

	rc = active_cacheline_insert(entry);

	if (rc == -ENOMEM) {

		pr_err("DMA-API: pfn tracking ENOMEM, dma-debug disabled\n");

		pr_err("DMA-API: cacheline tracking ENOMEM, dma-debug disabled\n");

		global_disable = true;

	}
@@ -631,7 +670,7 @@ static void dma_entry_free(struct dma_debug_entry *entry) 
{

	unsigned long flags;



	active_pfn_remove(entry);

	active_cacheline_remove(entry);



	/*

	 * add to beginning of the list - this way the entries are

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