[PATCH 0/4] dma-debug: implement dynamic entry allocation

[PATCH 0/4] dma-debug: implement dynamic entry allocation

[Robin Murphy]

The HNS_ENET discussion got me thinking, why not just make DMA debug
cleverer so that (in terms of basic functionality at least) we don't
need to worry about driver- or arch-specific configuration at all?

Patches #2 and #3 are the real meat here - #1 is just some preparatory
cleanup motivated by moving printks around, and could be split out if
desired; I kept #4 separate as a possible nice-to-have depending on
what people think.

Robin.


Robin Murphy (4):
  dma-debug: Use pr_fmt()
  dma-debug: Refactor dma_debug_entry allocation
  dma-debug: Dynamically expand the dma_debug_entry pool
  dma-debug: Make leak-like behaviour apparent

 kernel/dma/debug.c | 198 ++++++++++++++++++++++++---------------------
 1 file changed, 105 insertions(+), 93 deletions(-)

-- 
2.19.1.dirty

[PATCH 0/4] dma-debug: implement dynamic entry allocation

[Robin Murphy]

The HNS_ENET discussion got me thinking, why not just make DMA debug
cleverer so that (in terms of basic functionality at least) we don't
need to worry about driver- or arch-specific configuration at all?

Patches #2 and #3 are the real meat here - #1 is just some preparatory
cleanup motivated by moving printks around, and could be split out if
desired; I kept #4 separate as a possible nice-to-have depending on
what people think.

Robin.


Robin Murphy (4):
  dma-debug: Use pr_fmt()
  dma-debug: Refactor dma_debug_entry allocation
  dma-debug: Dynamically expand the dma_debug_entry pool
  dma-debug: Make leak-like behaviour apparent

 kernel/dma/debug.c | 198 ++++++++++++++++++++++++---------------------
 1 file changed, 105 insertions(+), 93 deletions(-)

-- 
2.19.1.dirty

[PATCH 1/4] dma-debug: Use pr_fmt()

[Robin Murphy]

Use pr_fmt() to generate the "DMA-API: " prefix consistently. This
results in it being added to a couple of pr_*() messages which were
missing it before, and for the err_printk() calls moves it to the actual
start of the message instead of somewhere in the middle.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

I chose not to refactor the existing split strings for minimal churn here.

 kernel/dma/debug.c | 74 ++++++++++++++++++++++++----------------------
 1 file changed, 38 insertions(+), 36 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 231ca4628062..91b84140e4a5 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -17,6 +17,8 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  */
 
+#define pr_fmt(fmt)	"DMA-API: " fmt
+
 #include <linux/sched/task_stack.h>
 #include <linux/scatterlist.h>
 #include <linux/dma-mapping.h>
@@ -234,7 +236,7 @@ static bool driver_filter(struct device *dev)
 		error_count += 1;					\
 		if (driver_filter(dev) &&				\
 		    (show_all_errors || show_num_errors > 0)) {		\
-			WARN(1, "%s %s: " format,			\
+			WARN(1, pr_fmt("%s %s: ") format,		\
 			     dev ? dev_driver_string(dev) : "NULL",	\
 			     dev ? dev_name(dev) : "NULL", ## arg);	\
 			dump_entry_trace(entry);			\
@@ -519,7 +521,7 @@ static void active_cacheline_inc_overlap(phys_addr_t cln)
 	 * prematurely.
 	 */
 	WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
-		  "DMA-API: exceeded %d overlapping mappings of cacheline %pa\n",
+		  pr_fmt("exceeded %d overlapping mappings of cacheline %pa\n"),
 		  ACTIVE_CACHELINE_MAX_OVERLAP, &cln);
 }
 
@@ -614,7 +616,7 @@ void debug_dma_assert_idle(struct page *page)
 
 	cln = to_cacheline_number(entry);
 	err_printk(entry->dev, entry,
-		   "DMA-API: cpu touching an active dma mapped cacheline [cln=%pa]\n",
+		   "cpu touching an active dma mapped cacheline [cln=%pa]\n",
 		   &cln);
 }
 
@@ -634,7 +636,7 @@ static void add_dma_entry(struct dma_debug_entry *entry)
 
 	rc = active_cacheline_insert(entry);
 	if (rc == -ENOMEM) {
-		pr_err("DMA-API: cacheline tracking ENOMEM, dma-debug disabled\n");
+		pr_err("cacheline tracking ENOMEM, dma-debug disabled\n");
 		global_disable = true;
 	}
 
@@ -673,7 +675,7 @@ static struct dma_debug_entry *dma_entry_alloc(void)
 	if (list_empty(&free_entries)) {
 		global_disable = true;
 		spin_unlock_irqrestore(&free_entries_lock, flags);
-		pr_err("DMA-API: debugging out of memory - disabling\n");
+		pr_err("debugging out of memory - disabling\n");
 		return NULL;
 	}
 
@@ -777,7 +779,7 @@ static int prealloc_memory(u32 num_entries)
 	num_free_entries = num_entries;
 	min_free_entries = num_entries;
 
-	pr_info("DMA-API: preallocated %d debug entries\n", num_entries);
+	pr_info("preallocated %d debug entries\n", num_entries);
 
 	return 0;
 
@@ -850,7 +852,7 @@ static ssize_t filter_write(struct file *file, const char __user *userbuf,
 		 * switched off.
 		 */
 		if (current_driver_name[0])
-			pr_info("DMA-API: switching off dma-debug driver filter\n");
+			pr_info("switching off dma-debug driver filter\n");
 		current_driver_name[0] = 0;
 		current_driver = NULL;
 		goto out_unlock;
@@ -868,7 +870,7 @@ static ssize_t filter_write(struct file *file, const char __user *userbuf,
 	current_driver_name[i] = 0;
 	current_driver = NULL;
 
-	pr_info("DMA-API: enable driver filter for driver [%s]\n",
+	pr_info("enable driver filter for driver [%s]\n",
 		current_driver_name);
 
 out_unlock:
@@ -887,7 +889,7 @@ static int dma_debug_fs_init(void)
 {
 	dma_debug_dent = debugfs_create_dir("dma-api", NULL);
 	if (!dma_debug_dent) {
-		pr_err("DMA-API: can not create debugfs directory\n");
+		pr_err("can not create debugfs directory\n");
 		return -ENOMEM;
 	}
 
@@ -973,7 +975,7 @@ static int dma_debug_device_change(struct notifier_block *nb, unsigned long acti
 		count = device_dma_allocations(dev, &entry);
 		if (count == 0)
 			break;
-		err_printk(dev, entry, "DMA-API: device driver has pending "
+		err_printk(dev, entry, "device driver has pending "
 				"DMA allocations while released from device "
 				"[count=%d]\n"
 				"One of leaked entries details: "
@@ -1023,14 +1025,14 @@ static int dma_debug_init(void)
 	}
 
 	if (dma_debug_fs_init() != 0) {
-		pr_err("DMA-API: error creating debugfs entries - disabling\n");
+		pr_err("error creating debugfs entries - disabling\n");
 		global_disable = true;
 
 		return 0;
 	}
 
 	if (prealloc_memory(nr_prealloc_entries) != 0) {
-		pr_err("DMA-API: debugging out of memory error - disabled\n");
+		pr_err("debugging out of memory error - disabled\n");
 		global_disable = true;
 
 		return 0;
@@ -1040,7 +1042,7 @@ static int dma_debug_init(void)
 
 	dma_debug_initialized = true;
 
-	pr_info("DMA-API: debugging enabled by kernel config\n");
+	pr_info("debugging enabled by kernel config\n");
 	return 0;
 }
 core_initcall(dma_debug_init);
@@ -1051,7 +1053,7 @@ static __init int dma_debug_cmdline(char *str)
 		return -EINVAL;
 
 	if (strncmp(str, "off", 3) == 0) {
-		pr_info("DMA-API: debugging disabled on kernel command line\n");
+		pr_info("debugging disabled on kernel command line\n");
 		global_disable = true;
 	}
 
@@ -1085,11 +1087,11 @@ static void check_unmap(struct dma_debug_entry *ref)
 
 		if (dma_mapping_error(ref->dev, ref->dev_addr)) {
 			err_printk(ref->dev, NULL,
-				   "DMA-API: device driver tries to free an "
+				   "device driver tries to free an "
 				   "invalid DMA memory address\n");
 		} else {
 			err_printk(ref->dev, NULL,
-				   "DMA-API: device driver tries to free DMA "
+				   "device driver tries to free DMA "
 				   "memory it has not allocated [device "
 				   "address=0x%016llx] [size=%llu bytes]\n",
 				   ref->dev_addr, ref->size);
@@ -1098,7 +1100,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 	}
 
 	if (ref->size != entry->size) {
-		err_printk(ref->dev, entry, "DMA-API: device driver frees "
+		err_printk(ref->dev, entry, "device driver frees "
 			   "DMA memory with different size "
 			   "[device address=0x%016llx] [map size=%llu bytes] "
 			   "[unmap size=%llu bytes]\n",
@@ -1106,7 +1108,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 	}
 
 	if (ref->type != entry->type) {
-		err_printk(ref->dev, entry, "DMA-API: device driver frees "
+		err_printk(ref->dev, entry, "device driver frees "
 			   "DMA memory with wrong function "
 			   "[device address=0x%016llx] [size=%llu bytes] "
 			   "[mapped as %s] [unmapped as %s]\n",
@@ -1114,7 +1116,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 			   type2name[entry->type], type2name[ref->type]);
 	} else if ((entry->type == dma_debug_coherent) &&
 		   (phys_addr(ref) != phys_addr(entry))) {
-		err_printk(ref->dev, entry, "DMA-API: device driver frees "
+		err_printk(ref->dev, entry, "device driver frees "
 			   "DMA memory with different CPU address "
 			   "[device address=0x%016llx] [size=%llu bytes] "
 			   "[cpu alloc address=0x%016llx] "
@@ -1126,7 +1128,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 
 	if (ref->sg_call_ents && ref->type == dma_debug_sg &&
 	    ref->sg_call_ents != entry->sg_call_ents) {
-		err_printk(ref->dev, entry, "DMA-API: device driver frees "
+		err_printk(ref->dev, entry, "device driver frees "
 			   "DMA sg list with different entry count "
 			   "[map count=%d] [unmap count=%d]\n",
 			   entry->sg_call_ents, ref->sg_call_ents);
@@ -1137,7 +1139,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 	 * DMA API don't handle this properly, so check for it here
 	 */
 	if (ref->direction != entry->direction) {
-		err_printk(ref->dev, entry, "DMA-API: device driver frees "
+		err_printk(ref->dev, entry, "device driver frees "
 			   "DMA memory with different direction "
 			   "[device address=0x%016llx] [size=%llu bytes] "
 			   "[mapped with %s] [unmapped with %s]\n",
@@ -1153,7 +1155,7 @@ static void check_unmap(struct dma_debug_entry *ref)
 	 */
 	if (entry->map_err_type == MAP_ERR_NOT_CHECKED) {
 		err_printk(ref->dev, entry,
-			   "DMA-API: device driver failed to check map error"
+			   "device driver failed to check map error"
 			   "[device address=0x%016llx] [size=%llu bytes] "
 			   "[mapped as %s]",
 			   ref->dev_addr, ref->size,
@@ -1178,7 +1180,7 @@ static void check_for_stack(struct device *dev,
 			return;
 		addr = page_address(page) + offset;
 		if (object_is_on_stack(addr))
-			err_printk(dev, NULL, "DMA-API: device driver maps memory from stack [addr=%p]\n", addr);
+			err_printk(dev, NULL, "device driver maps memory from stack [addr=%p]\n", addr);
 	} else {
 		/* Stack is vmalloced. */
 		int i;
@@ -1188,7 +1190,7 @@ static void check_for_stack(struct device *dev,
 				continue;
 
 			addr = (u8 *)current->stack + i * PAGE_SIZE + offset;
-			err_printk(dev, NULL, "DMA-API: device driver maps memory from stack [probable addr=%p]\n", addr);
+			err_printk(dev, NULL, "device driver maps memory from stack [probable addr=%p]\n", addr);
 			break;
 		}
 	}
@@ -1208,7 +1210,7 @@ static void check_for_illegal_area(struct device *dev, void *addr, unsigned long
 {
 	if (overlap(addr, len, _stext, _etext) ||
 	    overlap(addr, len, __start_rodata, __end_rodata))
-		err_printk(dev, NULL, "DMA-API: device driver maps memory from kernel text or rodata [addr=%p] [len=%lu]\n", addr, len);
+		err_printk(dev, NULL, "device driver maps memory from kernel text or rodata [addr=%p] [len=%lu]\n", addr, len);
 }
 
 static void check_sync(struct device *dev,
@@ -1224,7 +1226,7 @@ static void check_sync(struct device *dev,
 	entry = bucket_find_contain(&bucket, ref, &flags);
 
 	if (!entry) {
-		err_printk(dev, NULL, "DMA-API: device driver tries "
+		err_printk(dev, NULL, "device driver tries "
 				"to sync DMA memory it has not allocated "
 				"[device address=0x%016llx] [size=%llu bytes]\n",
 				(unsigned long long)ref->dev_addr, ref->size);
@@ -1232,7 +1234,7 @@ static void check_sync(struct device *dev,
 	}
 
 	if (ref->size > entry->size) {
-		err_printk(dev, entry, "DMA-API: device driver syncs"
+		err_printk(dev, entry, "device driver syncs"
 				" DMA memory outside allocated range "
 				"[device address=0x%016llx] "
 				"[allocation size=%llu bytes] "
@@ -1245,7 +1247,7 @@ static void check_sync(struct device *dev,
 		goto out;
 
 	if (ref->direction != entry->direction) {
-		err_printk(dev, entry, "DMA-API: device driver syncs "
+		err_printk(dev, entry, "device driver syncs "
 				"DMA memory with different direction "
 				"[device address=0x%016llx] [size=%llu bytes] "
 				"[mapped with %s] [synced with %s]\n",
@@ -1256,7 +1258,7 @@ static void check_sync(struct device *dev,
 
 	if (to_cpu && !(entry->direction == DMA_FROM_DEVICE) &&
 		      !(ref->direction == DMA_TO_DEVICE))
-		err_printk(dev, entry, "DMA-API: device driver syncs "
+		err_printk(dev, entry, "device driver syncs "
 				"device read-only DMA memory for cpu "
 				"[device address=0x%016llx] [size=%llu bytes] "
 				"[mapped with %s] [synced with %s]\n",
@@ -1266,7 +1268,7 @@ static void check_sync(struct device *dev,
 
 	if (!to_cpu && !(entry->direction == DMA_TO_DEVICE) &&
 		       !(ref->direction == DMA_FROM_DEVICE))
-		err_printk(dev, entry, "DMA-API: device driver syncs "
+		err_printk(dev, entry, "device driver syncs "
 				"device write-only DMA memory to device "
 				"[device address=0x%016llx] [size=%llu bytes] "
 				"[mapped with %s] [synced with %s]\n",
@@ -1276,7 +1278,7 @@ static void check_sync(struct device *dev,
 
 	if (ref->sg_call_ents && ref->type == dma_debug_sg &&
 	    ref->sg_call_ents != entry->sg_call_ents) {
-		err_printk(ref->dev, entry, "DMA-API: device driver syncs "
+		err_printk(ref->dev, entry, "device driver syncs "
 			   "DMA sg list with different entry count "
 			   "[map count=%d] [sync count=%d]\n",
 			   entry->sg_call_ents, ref->sg_call_ents);
@@ -1297,7 +1299,7 @@ static void check_sg_segment(struct device *dev, struct scatterlist *sg)
 	 * whoever generated the list forgot to check them.
 	 */
 	if (sg->length > max_seg)
-		err_printk(dev, NULL, "DMA-API: mapping sg segment longer than device claims to support [len=%u] [max=%u]\n",
+		err_printk(dev, NULL, "mapping sg segment longer than device claims to support [len=%u] [max=%u]\n",
 			   sg->length, max_seg);
 	/*
 	 * In some cases this could potentially be the DMA API
@@ -1307,7 +1309,7 @@ static void check_sg_segment(struct device *dev, struct scatterlist *sg)
 	start = sg_dma_address(sg);
 	end = start + sg_dma_len(sg) - 1;
 	if ((start ^ end) & ~boundary)
-		err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
+		err_printk(dev, NULL, "mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
 			   start, end, boundary);
 #endif
 }
@@ -1319,11 +1321,11 @@ void debug_dma_map_single(struct device *dev, const void *addr,
 		return;
 
 	if (!virt_addr_valid(addr))
-		err_printk(dev, NULL, "DMA-API: device driver maps memory from invalid area [addr=%p] [len=%lu]\n",
+		err_printk(dev, NULL, "device driver maps memory from invalid area [addr=%p] [len=%lu]\n",
 			   addr, len);
 
 	if (is_vmalloc_addr(addr))
-		err_printk(dev, NULL, "DMA-API: device driver maps memory from vmalloc area [addr=%p] [len=%lu]\n",
+		err_printk(dev, NULL, "device driver maps memory from vmalloc area [addr=%p] [len=%lu]\n",
 			   addr, len);
 }
 EXPORT_SYMBOL(debug_dma_map_single);
@@ -1780,7 +1782,7 @@ static int __init dma_debug_driver_setup(char *str)
 	}
 
 	if (current_driver_name[0])
-		pr_info("DMA-API: enable driver filter for driver [%s]\n",
+		pr_info("enable driver filter for driver [%s]\n",
 			current_driver_name);
 
 
-- 
2.19.1.dirty

Re: [PATCH 1/4] dma-debug: Use pr_fmt()

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 1/4] dma-debug: Use pr_fmt()

[Joe Perches]

On Mon, 2018-12-03 at 17:28 +0000, Robin Murphy wrote:
> Use pr_fmt() to generate the "DMA-API: " prefix consistently. This
> results in it being added to a couple of pr_*() messages which were
> missing it before, and for the err_printk() calls moves it to the actual
> start of the message instead of somewhere in the middle.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> 
> I chose not to refactor the existing split strings for minimal churn here.
> 
>  kernel/dma/debug.c | 74 ++++++++++++++++++++++++----------------------
>  1 file changed, 38 insertions(+), 36 deletions(-)
> 
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index 231ca4628062..91b84140e4a5 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -17,6 +17,8 @@
>   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
>   */
>  
> +#define pr_fmt(fmt)	"DMA-API: " fmt
> +
>  #include <linux/sched/task_stack.h>
>  #include <linux/scatterlist.h>
>  #include <linux/dma-mapping.h>
> @@ -234,7 +236,7 @@ static bool driver_filter(struct device *dev)
>  		error_count += 1;					\
>  		if (driver_filter(dev) &&				\
>  		    (show_all_errors || show_num_errors > 0)) {		\
> -			WARN(1, "%s %s: " format,			\
> +			WARN(1, pr_fmt("%s %s: ") format,		\
>  			     dev ? dev_driver_string(dev) : "NULL",	\
>  			     dev ? dev_name(dev) : "NULL", ## arg);	\
>  			dump_entry_trace(entry);			\

I think converting this WARN to

			dev_err(dev, format, ##__VA_ARGS__);
			dump_stack();

would look better and be more intelligible.

Perhaps add a #define for dev_fmt if really necessary.

[PATCH 2/4] dma-debug: Refactor dma_debug_entry allocation

[Robin Murphy]

Make prealloc_memory() a little more general and robust so that it
serves for runtime reallocations too. The first thing we can do with
that is clean up dma_debug_resize_entries() quite a bit.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 kernel/dma/debug.c | 95 +++++++++++++++++++---------------------------
 1 file changed, 40 insertions(+), 55 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 91b84140e4a5..de5db800dbfc 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -645,6 +645,39 @@ static void add_dma_entry(struct dma_debug_entry *entry)
 	 */
 }
 
+static int prealloc_memory(u32 num_entries)
+{
+	struct dma_debug_entry *entry, *next_entry;
+	unsigned long flags;
+	LIST_HEAD(tmp);
+	int i;
+
+	for (i = 0; i < num_entries; ++i) {
+		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+		if (!entry)
+			goto out_err;
+
+		list_add_tail(&entry->list, &tmp);
+	}
+
+	spin_lock_irqsave(&free_entries_lock, flags);
+	list_splice(&tmp, &free_entries);
+	num_free_entries += num_entries;
+	nr_total_entries += num_entries;
+	spin_unlock_irqrestore(&free_entries_lock, flags);
+
+	return 0;
+
+out_err:
+
+	list_for_each_entry_safe(entry, next_entry, &tmp, list) {
+		list_del(&entry->list);
+		kfree(entry);
+	}
+
+	return -ENOMEM;
+}
+
 static struct dma_debug_entry *__dma_entry_alloc(void)
 {
 	struct dma_debug_entry *entry;
@@ -714,44 +747,25 @@ int dma_debug_resize_entries(u32 num_entries)
 	int i, delta, ret = 0;
 	unsigned long flags;
 	struct dma_debug_entry *entry;
-	LIST_HEAD(tmp);
-
-	spin_lock_irqsave(&free_entries_lock, flags);
 
 	if (nr_total_entries < num_entries) {
 		delta = num_entries - nr_total_entries;
 
-		spin_unlock_irqrestore(&free_entries_lock, flags);
-
-		for (i = 0; i < delta; i++) {
-			entry = kzalloc(sizeof(*entry), GFP_KERNEL);
-			if (!entry)
-				break;
-
-			list_add_tail(&entry->list, &tmp);
-		}
-
-		spin_lock_irqsave(&free_entries_lock, flags);
-
-		list_splice(&tmp, &free_entries);
-		nr_total_entries += i;
-		num_free_entries += i;
+		ret = prealloc_memory(delta);
 	} else {
 		delta = nr_total_entries - num_entries;
 
+		spin_lock_irqsave(&free_entries_lock, flags);
 		for (i = 0; i < delta && !list_empty(&free_entries); i++) {
 			entry = __dma_entry_alloc();
 			kfree(entry);
 		}
+		spin_unlock_irqrestore(&free_entries_lock, flags);
 
 		nr_total_entries -= i;
+		if (nr_total_entries != num_entries)
+			ret = -EBUSY;
 	}
-
-	if (nr_total_entries != num_entries)
-		ret = 1;
-
-	spin_unlock_irqrestore(&free_entries_lock, flags);
-
 	return ret;
 }
 
@@ -763,36 +777,6 @@ int dma_debug_resize_entries(u32 num_entries)
  *   2. Preallocate a given number of dma_debug_entry structs
  */
 
-static int prealloc_memory(u32 num_entries)
-{
-	struct dma_debug_entry *entry, *next_entry;
-	int i;
-
-	for (i = 0; i < num_entries; ++i) {
-		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
-		if (!entry)
-			goto out_err;
-
-		list_add_tail(&entry->list, &free_entries);
-	}
-
-	num_free_entries = num_entries;
-	min_free_entries = num_entries;
-
-	pr_info("preallocated %d debug entries\n", num_entries);
-
-	return 0;
-
-out_err:
-
-	list_for_each_entry_safe(entry, next_entry, &free_entries, list) {
-		list_del(&entry->list);
-		kfree(entry);
-	}
-
-	return -ENOMEM;
-}
-
 static ssize_t filter_read(struct file *file, char __user *user_buf,
 			   size_t count, loff_t *ppos)
 {
@@ -1038,7 +1022,8 @@ static int dma_debug_init(void)
 		return 0;
 	}
 
-	nr_total_entries = num_free_entries;
+	min_free_entries = num_free_entries;
+	pr_info("preallocated %d debug entries\n", nr_total_entries);
 
 	dma_debug_initialized = true;
 
-- 
2.19.1.dirty

Re: [PATCH 2/4] dma-debug: Refactor dma_debug_entry allocation

[Christoph Hellwig]

On Mon, Dec 03, 2018 at 05:28:07PM +0000, Robin Murphy wrote:
> Make prealloc_memory() a little more general and robust so that it
> serves for runtime reallocations too. The first thing we can do with
> that is clean up dma_debug_resize_entries() quite a bit.

Maybe also renamed it to dma_debug_alloc_entries or something like
that?

Otherwise this looks fine to me.

Re: [PATCH 2/4] dma-debug: Refactor dma_debug_entry allocation

[Robin Murphy]

On 04/12/2018 14:27, Christoph Hellwig wrote:
> On Mon, Dec 03, 2018 at 05:28:07PM +0000, Robin Murphy wrote:
>> Make prealloc_memory() a little more general and robust so that it
>> serves for runtime reallocations too. The first thing we can do with
>> that is clean up dma_debug_resize_entries() quite a bit.
> 
> Maybe also renamed it to dma_debug_alloc_entries or something like
> that?

Yes, that's definitely nicer.

> Otherwise this looks fine to me.

Thanks (and for the review on #1)

Robin.

Re: [PATCH 2/4] dma-debug: Refactor dma_debug_entry allocation

[Robin Murphy]

On 04/12/2018 14:27, Christoph Hellwig wrote:
> On Mon, Dec 03, 2018 at 05:28:07PM +0000, Robin Murphy wrote:
>> Make prealloc_memory() a little more general and robust so that it
>> serves for runtime reallocations too. The first thing we can do with
>> that is clean up dma_debug_resize_entries() quite a bit.
> 
> Maybe also renamed it to dma_debug_alloc_entries or something like
> that?

Yes, that's definitely nicer.

> Otherwise this looks fine to me.

Thanks (and for the review on #1)

Robin.

[PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

Certain drivers such as large multi-queue network adapters can use pools
of mapped DMA buffers larger than the default dma_debug_entry pool of
65536 entries, with the result that merely probing such a device can
cause DMA debug to disable itself during boot unless explicitly given an
appropriate "dma_debug_entries=..." option.

Developers trying to debug some other driver on such a system may not be
immediately aware of this, and at worst it can hide bugs if they fail to
realise that dma-debug has already disabled itself unexpectedly by the
time the code of interest gets to run. Even once they do realise, it can
be a bit of a pain to emprirically determine a suitable number of
preallocated entries to configure without massively over-allocating.

There's really no need for such a static limit, though, since we can
quite easily expand the pool at runtime in those rare cases that the
preallocated entries are insufficient, which is arguably the least
surprising and most useful behaviour.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 kernel/dma/debug.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index de5db800dbfc..46cc075aec99 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -47,6 +47,9 @@
 #ifndef PREALLOC_DMA_DEBUG_ENTRIES
 #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
 #endif
+/* If the pool runs out, try this many times to allocate this many new entries */
+#define DMA_DEBUG_DYNAMIC_ENTRIES 256
+#define DMA_DEBUG_DYNAMIC_RETRIES 2
 
 enum {
 	dma_debug_single,
@@ -702,12 +705,21 @@ static struct dma_debug_entry *dma_entry_alloc(void)
 {
 	struct dma_debug_entry *entry;
 	unsigned long flags;
+	int retry_count;
 
-	spin_lock_irqsave(&free_entries_lock, flags);
+	for (retry_count = 0; ; retry_count++) {
+		spin_lock_irqsave(&free_entries_lock, flags);
+
+		if (num_free_entries > 0)
+			break;
 
-	if (list_empty(&free_entries)) {
-		global_disable = true;
 		spin_unlock_irqrestore(&free_entries_lock, flags);
+
+		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
+		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
+			continue;
+
+		global_disable = true;
 		pr_err("debugging out of memory - disabling\n");
 		return NULL;
 	}
-- 
2.19.1.dirty

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

On 03/12/2018 17:28, Robin Murphy wrote:
> Certain drivers such as large multi-queue network adapters can use pools
> of mapped DMA buffers larger than the default dma_debug_entry pool of
> 65536 entries, with the result that merely probing such a device can
> cause DMA debug to disable itself during boot unless explicitly given an
> appropriate "dma_debug_entries=..." option.
>
> Developers trying to debug some other driver on such a system may not be
> immediately aware of this, and at worst it can hide bugs if they fail to
> realise that dma-debug has already disabled itself unexpectedly by the
> time the code of interest gets to run. Even once they do realise, it can
> be a bit of a pain to emprirically determine a suitable number of
> preallocated entries to configure without massively over-allocating.
>
> There's really no need for such a static limit, though, since we can
> quite easily expand the pool at runtime in those rare cases that the
> preallocated entries are insufficient, which is arguably the least
> surprising and most useful behaviour.

Hi Robin,

Do you have an idea on shrinking the pool again when the culprit driver 
is removed, i.e. we have so many unused debug entries now available?

Thanks,
John

>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  kernel/dma/debug.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index de5db800dbfc..46cc075aec99 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -47,6 +47,9 @@
>  #ifndef PREALLOC_DMA_DEBUG_ENTRIES
>  #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
>  #endif
> +/* If the pool runs out, try this many times to allocate this many new entries */
> +#define DMA_DEBUG_DYNAMIC_ENTRIES 256
> +#define DMA_DEBUG_DYNAMIC_RETRIES 2
>
>  enum {
>  	dma_debug_single,
> @@ -702,12 +705,21 @@ static struct dma_debug_entry *dma_entry_alloc(void)
>  {
>  	struct dma_debug_entry *entry;
>  	unsigned long flags;
> +	int retry_count;
>
> -	spin_lock_irqsave(&free_entries_lock, flags);
> +	for (retry_count = 0; ; retry_count++) {
> +		spin_lock_irqsave(&free_entries_lock, flags);
> +
> +		if (num_free_entries > 0)
> +			break;
>
> -	if (list_empty(&free_entries)) {
> -		global_disable = true;
>  		spin_unlock_irqrestore(&free_entries_lock, flags);
> +
> +		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
> +		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
> +			continue;
> +
> +		global_disable = true;
>  		pr_err("debugging out of memory - disabling\n");
>  		return NULL;
>  	}
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

On 03/12/2018 17:28, Robin Murphy wrote:
> Certain drivers such as large multi-queue network adapters can use pools
> of mapped DMA buffers larger than the default dma_debug_entry pool of
> 65536 entries, with the result that merely probing such a device can
> cause DMA debug to disable itself during boot unless explicitly given an
> appropriate "dma_debug_entries=..." option.
>
> Developers trying to debug some other driver on such a system may not be
> immediately aware of this, and at worst it can hide bugs if they fail to
> realise that dma-debug has already disabled itself unexpectedly by the
> time the code of interest gets to run. Even once they do realise, it can
> be a bit of a pain to emprirically determine a suitable number of
> preallocated entries to configure without massively over-allocating.
>
> There's really no need for such a static limit, though, since we can
> quite easily expand the pool at runtime in those rare cases that the
> preallocated entries are insufficient, which is arguably the least
> surprising and most useful behaviour.

Hi Robin,

Do you have an idea on shrinking the pool again when the culprit driver 
is removed, i.e. we have so many unused debug entries now available?

Thanks,
John

>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  kernel/dma/debug.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index de5db800dbfc..46cc075aec99 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -47,6 +47,9 @@
>  #ifndef PREALLOC_DMA_DEBUG_ENTRIES
>  #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
>  #endif
> +/* If the pool runs out, try this many times to allocate this many new entries */
> +#define DMA_DEBUG_DYNAMIC_ENTRIES 256
> +#define DMA_DEBUG_DYNAMIC_RETRIES 2
>
>  enum {
>  	dma_debug_single,
> @@ -702,12 +705,21 @@ static struct dma_debug_entry *dma_entry_alloc(void)
>  {
>  	struct dma_debug_entry *entry;
>  	unsigned long flags;
> +	int retry_count;
>
> -	spin_lock_irqsave(&free_entries_lock, flags);
> +	for (retry_count = 0; ; retry_count++) {
> +		spin_lock_irqsave(&free_entries_lock, flags);
> +
> +		if (num_free_entries > 0)
> +			break;
>
> -	if (list_empty(&free_entries)) {
> -		global_disable = true;
>  		spin_unlock_irqrestore(&free_entries_lock, flags);
> +
> +		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
> +		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
> +			continue;
> +
> +		global_disable = true;
>  		pr_err("debugging out of memory - disabling\n");
>  		return NULL;
>  	}
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

Hi John,

On 03/12/2018 18:23, John Garry wrote:
> On 03/12/2018 17:28, Robin Murphy wrote:
>> Certain drivers such as large multi-queue network adapters can use pools
>> of mapped DMA buffers larger than the default dma_debug_entry pool of
>> 65536 entries, with the result that merely probing such a device can
>> cause DMA debug to disable itself during boot unless explicitly given an
>> appropriate "dma_debug_entries=..." option.
>>
>> Developers trying to debug some other driver on such a system may not be
>> immediately aware of this, and at worst it can hide bugs if they fail to
>> realise that dma-debug has already disabled itself unexpectedly by the
>> time the code of interest gets to run. Even once they do realise, it can
>> be a bit of a pain to emprirically determine a suitable number of
>> preallocated entries to configure without massively over-allocating.
>>
>> There's really no need for such a static limit, though, since we can
>> quite easily expand the pool at runtime in those rare cases that the
>> preallocated entries are insufficient, which is arguably the least
>> surprising and most useful behaviour.
> 
> Hi Robin,
> 
> Do you have an idea on shrinking the pool again when the culprit driver 
> is removed, i.e. we have so many unused debug entries now available?

I honestly don't believe it's worth the complication. This is a 
development feature with significant overheads already, so there's not 
an awful lot to gain by trying to optimise memory usage. If a system can 
ever load a driver that makes hundreds of thousands of simultaneous 
mappings, it can almost certainly spare 20-odd megabytes of RAM for the 
corresponding debug entries in perpetuity. Sure, it does mean you'd need 
to reboot to recover memory from a major leak, but that's mostly true of 
the current behaviour too, and rebooting during driver development is 
hardly an unacceptable inconvenience.

In fact, having got this far in, what I'd quite like to do is to get rid 
of dma_debug_resize_entries() such that we never need to free things at 
all, since then we could allocate whole pages as blocks of entries to 
save on masses of individual slab allocations.

Robin.

> 
> Thanks,
> John
> 
>>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>  kernel/dma/debug.c | 18 +++++++++++++++---
>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
>> index de5db800dbfc..46cc075aec99 100644
>> --- a/kernel/dma/debug.c
>> +++ b/kernel/dma/debug.c
>> @@ -47,6 +47,9 @@
>>  #ifndef PREALLOC_DMA_DEBUG_ENTRIES
>>  #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
>>  #endif
>> +/* If the pool runs out, try this many times to allocate this many 
>> new entries */
>> +#define DMA_DEBUG_DYNAMIC_ENTRIES 256
>> +#define DMA_DEBUG_DYNAMIC_RETRIES 2
>>
>>  enum {
>>      dma_debug_single,
>> @@ -702,12 +705,21 @@ static struct dma_debug_entry 
>> *dma_entry_alloc(void)
>>  {
>>      struct dma_debug_entry *entry;
>>      unsigned long flags;
>> +    int retry_count;
>>
>> -    spin_lock_irqsave(&free_entries_lock, flags);
>> +    for (retry_count = 0; ; retry_count++) {
>> +        spin_lock_irqsave(&free_entries_lock, flags);
>> +
>> +        if (num_free_entries > 0)
>> +            break;
>>
>> -    if (list_empty(&free_entries)) {
>> -        global_disable = true;
>>          spin_unlock_irqrestore(&free_entries_lock, flags);
>> +
>> +        if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
>> +            !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
>> +            continue;
>> +
>> +        global_disable = true;
>>          pr_err("debugging out of memory - disabling\n");
>>          return NULL;
>>      }
>>
> 
> 

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Christoph Hellwig]

On Tue, Dec 04, 2018 at 01:11:37PM +0000, Robin Murphy wrote:
> In fact, having got this far in, what I'd quite like to do is to get rid of 
> dma_debug_resize_entries() such that we never need to free things at all, 
> since then we could allocate whole pages as blocks of entries to save on 
> masses of individual slab allocations.

Yes, we should defintively kill dma_debug_resize_entries.  Allocating
page batches might sound nice, but is that going to introduce additional
complexity?

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

On 04/12/2018 14:17, Christoph Hellwig wrote:
> On Tue, Dec 04, 2018 at 01:11:37PM +0000, Robin Murphy wrote:
>> In fact, having got this far in, what I'd quite like to do is to get rid of
>> dma_debug_resize_entries() such that we never need to free things at all,
>> since then we could allocate whole pages as blocks of entries to save on
>> masses of individual slab allocations.
> 
> Yes, we should defintively kill dma_debug_resize_entries.  Allocating
> page batches might sound nice, but is that going to introduce additional
> complexity?

OK, looking at what the weird AMD GART code does I reckon it should be 
happy enough with on-demand expansion, and that no tears will be shed if 
it can no longer actually trim the pool to the size it thinks is 
necessary. I'll add a patch to clean that up.

Page-based allocation, at least the way I'm thinking of it, shouldn't do 
much more than add an extra loop in one place, which should be more than 
made up for by removing all the freeing code :)

Robin.

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

On 04/12/2018 13:11, Robin Murphy wrote:
> Hi John,
>
> On 03/12/2018 18:23, John Garry wrote:
>> On 03/12/2018 17:28, Robin Murphy wrote:
>>> Certain drivers such as large multi-queue network adapters can use pools
>>> of mapped DMA buffers larger than the default dma_debug_entry pool of
>>> 65536 entries, with the result that merely probing such a device can
>>> cause DMA debug to disable itself during boot unless explicitly given an
>>> appropriate "dma_debug_entries=..." option.
>>>
>>> Developers trying to debug some other driver on such a system may not be
>>> immediately aware of this, and at worst it can hide bugs if they fail to
>>> realise that dma-debug has already disabled itself unexpectedly by the
>>> time the code of interest gets to run. Even once they do realise, it can
>>> be a bit of a pain to emprirically determine a suitable number of
>>> preallocated entries to configure without massively over-allocating.
>>>
>>> There's really no need for such a static limit, though, since we can
>>> quite easily expand the pool at runtime in those rare cases that the
>>> preallocated entries are insufficient, which is arguably the least
>>> surprising and most useful behaviour.
>>
>> Hi Robin,
>>
>> Do you have an idea on shrinking the pool again when the culprit
>> driver is removed, i.e. we have so many unused debug entries now
>> available?
>
> I honestly don't believe it's worth the complication. This is a
> development feature with significant overheads already, so there's not
> an awful lot to gain by trying to optimise memory usage. If a system can
> ever load a driver that makes hundreds of thousands of simultaneous
> mappings, it can almost certainly spare 20-odd megabytes of RAM for the
> corresponding debug entries in perpetuity. Sure, it does mean you'd need
> to reboot to recover memory from a major leak, but that's mostly true of
> the current behaviour too, and rebooting during driver development is
> hardly an unacceptable inconvenience.
>

ok, I just thought that it would not be too difficult to implement this 
on the dma entry free path.

> In fact, having got this far in, what I'd quite like to do is to get rid
> of dma_debug_resize_entries() such that we never need to free things at
> all, since then we could allocate whole pages as blocks of entries to
> save on masses of individual slab allocations.
>

On a related topic, is it possible for the user to learn the total 
entries created at a given point in time? If not, could we add a file in 
the debugfs folder for this?

Thanks,
John

> Robin.
>
>>
>> Thanks,
>> John
>>
>>>
>>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>>> ---
>>>  kernel/dma/debug.c | 18 +++++++++++++++---
>>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
>>> index de5db800dbfc..46cc075aec99 100644
>>> --- a/kernel/dma/debug.c
>>> +++ b/kernel/dma/debug.c
>>> @@ -47,6 +47,9 @@
>>>  #ifndef PREALLOC_DMA_DEBUG_ENTRIES
>>>  #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
>>>  #endif
>>> +/* If the pool runs out, try this many times to allocate this many
>>> new entries */
>>> +#define DMA_DEBUG_DYNAMIC_ENTRIES 256
>>> +#define DMA_DEBUG_DYNAMIC_RETRIES 2
>>>
>>>  enum {
>>>      dma_debug_single,
>>> @@ -702,12 +705,21 @@ static struct dma_debug_entry
>>> *dma_entry_alloc(void)
>>>  {
>>>      struct dma_debug_entry *entry;
>>>      unsigned long flags;
>>> +    int retry_count;
>>>
>>> -    spin_lock_irqsave(&free_entries_lock, flags);
>>> +    for (retry_count = 0; ; retry_count++) {
>>> +        spin_lock_irqsave(&free_entries_lock, flags);
>>> +
>>> +        if (num_free_entries > 0)
>>> +            break;
>>>
>>> -    if (list_empty(&free_entries)) {
>>> -        global_disable = true;
>>>          spin_unlock_irqrestore(&free_entries_lock, flags);
>>> +
>>> +        if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
>>> +            !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
>>> +            continue;
>>> +
>>> +        global_disable = true;
>>>          pr_err("debugging out of memory - disabling\n");
>>>          return NULL;
>>>      }
>>>
>>
>>
>
> .
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

On 04/12/2018 13:11, Robin Murphy wrote:
> Hi John,
>
> On 03/12/2018 18:23, John Garry wrote:
>> On 03/12/2018 17:28, Robin Murphy wrote:
>>> Certain drivers such as large multi-queue network adapters can use pools
>>> of mapped DMA buffers larger than the default dma_debug_entry pool of
>>> 65536 entries, with the result that merely probing such a device can
>>> cause DMA debug to disable itself during boot unless explicitly given an
>>> appropriate "dma_debug_entries=..." option.
>>>
>>> Developers trying to debug some other driver on such a system may not be
>>> immediately aware of this, and at worst it can hide bugs if they fail to
>>> realise that dma-debug has already disabled itself unexpectedly by the
>>> time the code of interest gets to run. Even once they do realise, it can
>>> be a bit of a pain to emprirically determine a suitable number of
>>> preallocated entries to configure without massively over-allocating.
>>>
>>> There's really no need for such a static limit, though, since we can
>>> quite easily expand the pool at runtime in those rare cases that the
>>> preallocated entries are insufficient, which is arguably the least
>>> surprising and most useful behaviour.
>>
>> Hi Robin,
>>
>> Do you have an idea on shrinking the pool again when the culprit
>> driver is removed, i.e. we have so many unused debug entries now
>> available?
>
> I honestly don't believe it's worth the complication. This is a
> development feature with significant overheads already, so there's not
> an awful lot to gain by trying to optimise memory usage. If a system can
> ever load a driver that makes hundreds of thousands of simultaneous
> mappings, it can almost certainly spare 20-odd megabytes of RAM for the
> corresponding debug entries in perpetuity. Sure, it does mean you'd need
> to reboot to recover memory from a major leak, but that's mostly true of
> the current behaviour too, and rebooting during driver development is
> hardly an unacceptable inconvenience.
>

ok, I just thought that it would not be too difficult to implement this 
on the dma entry free path.

> In fact, having got this far in, what I'd quite like to do is to get rid
> of dma_debug_resize_entries() such that we never need to free things at
> all, since then we could allocate whole pages as blocks of entries to
> save on masses of individual slab allocations.
>

On a related topic, is it possible for the user to learn the total 
entries created at a given point in time? If not, could we add a file in 
the debugfs folder for this?

Thanks,
John

> Robin.
>
>>
>> Thanks,
>> John
>>
>>>
>>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>>> ---
>>>  kernel/dma/debug.c | 18 +++++++++++++++---
>>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
>>> index de5db800dbfc..46cc075aec99 100644
>>> --- a/kernel/dma/debug.c
>>> +++ b/kernel/dma/debug.c
>>> @@ -47,6 +47,9 @@
>>>  #ifndef PREALLOC_DMA_DEBUG_ENTRIES
>>>  #define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
>>>  #endif
>>> +/* If the pool runs out, try this many times to allocate this many
>>> new entries */
>>> +#define DMA_DEBUG_DYNAMIC_ENTRIES 256
>>> +#define DMA_DEBUG_DYNAMIC_RETRIES 2
>>>
>>>  enum {
>>>      dma_debug_single,
>>> @@ -702,12 +705,21 @@ static struct dma_debug_entry
>>> *dma_entry_alloc(void)
>>>  {
>>>      struct dma_debug_entry *entry;
>>>      unsigned long flags;
>>> +    int retry_count;
>>>
>>> -    spin_lock_irqsave(&free_entries_lock, flags);
>>> +    for (retry_count = 0; ; retry_count++) {
>>> +        spin_lock_irqsave(&free_entries_lock, flags);
>>> +
>>> +        if (num_free_entries > 0)
>>> +            break;
>>>
>>> -    if (list_empty(&free_entries)) {
>>> -        global_disable = true;
>>>          spin_unlock_irqrestore(&free_entries_lock, flags);
>>> +
>>> +        if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
>>> +            !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
>>> +            continue;
>>> +
>>> +        global_disable = true;
>>>          pr_err("debugging out of memory - disabling\n");
>>>          return NULL;
>>>      }
>>>
>>
>>
>
> .
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

On 04/12/2018 16:30, John Garry wrote:
> On 04/12/2018 13:11, Robin Murphy wrote:
>> Hi John,
>>
>> On 03/12/2018 18:23, John Garry wrote:
>>> On 03/12/2018 17:28, Robin Murphy wrote:
>>>> Certain drivers such as large multi-queue network adapters can use 
>>>> pools
>>>> of mapped DMA buffers larger than the default dma_debug_entry pool of
>>>> 65536 entries, with the result that merely probing such a device can
>>>> cause DMA debug to disable itself during boot unless explicitly 
>>>> given an
>>>> appropriate "dma_debug_entries=..." option.
>>>>
>>>> Developers trying to debug some other driver on such a system may 
>>>> not be
>>>> immediately aware of this, and at worst it can hide bugs if they 
>>>> fail to
>>>> realise that dma-debug has already disabled itself unexpectedly by the
>>>> time the code of interest gets to run. Even once they do realise, it 
>>>> can
>>>> be a bit of a pain to emprirically determine a suitable number of
>>>> preallocated entries to configure without massively over-allocating.
>>>>
>>>> There's really no need for such a static limit, though, since we can
>>>> quite easily expand the pool at runtime in those rare cases that the
>>>> preallocated entries are insufficient, which is arguably the least
>>>> surprising and most useful behaviour.
>>>
>>> Hi Robin,
>>>
>>> Do you have an idea on shrinking the pool again when the culprit
>>> driver is removed, i.e. we have so many unused debug entries now
>>> available?
>>
>> I honestly don't believe it's worth the complication. This is a
>> development feature with significant overheads already, so there's not
>> an awful lot to gain by trying to optimise memory usage. If a system can
>> ever load a driver that makes hundreds of thousands of simultaneous
>> mappings, it can almost certainly spare 20-odd megabytes of RAM for the
>> corresponding debug entries in perpetuity. Sure, it does mean you'd need
>> to reboot to recover memory from a major leak, but that's mostly true of
>> the current behaviour too, and rebooting during driver development is
>> hardly an unacceptable inconvenience.
>>
> 
> ok, I just thought that it would not be too difficult to implement this 
> on the dma entry free path.

True, in the current code it wouldn't be all that hard, but it feels 
more worthwhile to optimise for allocation rather than freeing, and as 
soon as we start allocating memory for multiple entries at once, trying 
to free anything becomes extremely challenging.

>> In fact, having got this far in, what I'd quite like to do is to get rid
>> of dma_debug_resize_entries() such that we never need to free things at
>> all, since then we could allocate whole pages as blocks of entries to
>> save on masses of individual slab allocations.
>>
> 
> On a related topic, is it possible for the user to learn the total 
> entries created at a given point in time? If not, could we add a file in 
> the debugfs folder for this?

I did get as far as pondering that you effectively lose track of 
utilisation once the low-water-mark of min_free_entries hits 0 and stays 
there - AFAICS it should be sufficient to just expose nr_total_entries 
as-is, since users can then calculate current and maximum occupancy 
based on *_free_entries. Does that sound reasonable to you?

That also indirectly reminds me that this lot is documented in 
DMA_API.txt, so I should be good and update that too...

Cheers,
Robin.

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

>
>>> In fact, having got this far in, what I'd quite like to do is to get rid
>>> of dma_debug_resize_entries() such that we never need to free things at
>>> all, since then we could allocate whole pages as blocks of entries to
>>> save on masses of individual slab allocations.
>>>
>>
>> On a related topic, is it possible for the user to learn the total
>> entries created at a given point in time? If not, could we add a file
>> in the debugfs folder for this?
>

Hi Robin,

> I did get as far as pondering that you effectively lose track of
> utilisation once the low-water-mark of min_free_entries hits 0 and stays

I did try your patches and I noticed this, i.e I was hitting the point 
at which we start to alloc more entries.

> there - AFAICS it should be sufficient to just expose nr_total_entries
> as-is, since users can then calculate current and maximum occupancy
> based on *_free_entries. Does that sound reasonable to you?
>

Sounds ok. I am just interested to know roughly how many DMA buffers 
we're using in our system.

> That also indirectly reminds me that this lot is documented in
> DMA_API.txt, so I should be good and update that too...

Thanks,
John

>
> Cheers,
> Robin.
>
> .
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[John Garry]

>
>>> In fact, having got this far in, what I'd quite like to do is to get rid
>>> of dma_debug_resize_entries() such that we never need to free things at
>>> all, since then we could allocate whole pages as blocks of entries to
>>> save on masses of individual slab allocations.
>>>
>>
>> On a related topic, is it possible for the user to learn the total
>> entries created at a given point in time? If not, could we add a file
>> in the debugfs folder for this?
>

Hi Robin,

> I did get as far as pondering that you effectively lose track of
> utilisation once the low-water-mark of min_free_entries hits 0 and stays

I did try your patches and I noticed this, i.e I was hitting the point 
at which we start to alloc more entries.

> there - AFAICS it should be sufficient to just expose nr_total_entries
> as-is, since users can then calculate current and maximum occupancy
> based on *_free_entries. Does that sound reasonable to you?
>

Sounds ok. I am just interested to know roughly how many DMA buffers 
we're using in our system.

> That also indirectly reminds me that this lot is documented in
> DMA_API.txt, so I should be good and update that too...

Thanks,
John

>
> Cheers,
> Robin.
>
> .
>

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Christoph Hellwig]

> +	for (retry_count = 0; ; retry_count++) {
> +		spin_lock_irqsave(&free_entries_lock, flags);
> +
> +		if (num_free_entries > 0)
> +			break;
>  
>  		spin_unlock_irqrestore(&free_entries_lock, flags);

Taking a spinlock just to read a single integer value doesn't really
help anything.

> +
> +		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
> +		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))

Don't we need GFP_ATOMIC here?  Also why do we need the retries?

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

On 04/12/2018 14:29, Christoph Hellwig wrote:
>> +	for (retry_count = 0; ; retry_count++) {
>> +		spin_lock_irqsave(&free_entries_lock, flags);
>> +
>> +		if (num_free_entries > 0)
>> +			break;
>>   
>>   		spin_unlock_irqrestore(&free_entries_lock, flags);
> 
> Taking a spinlock just to read a single integer value doesn't really
> help anything.

If the freelist is non-empty we break out with the lock still held in 
order to actually allocate our entry - only if there are no free entries 
left do we drop the lock in order to handle the failure. This much is 
just the original logic shuffled around a bit (with the tweak that 
testing num_free_entries seemed justifiably simpler than the original 
list_empty() check).

>> +
>> +		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
>> +		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
> 
> Don't we need GFP_ATOMIC here?  Also why do we need the retries?

Ah, right, we may be outside our own spinlock, but of course the whole 
DMA API call which got us here might be under someone else's and/or in a 
non-sleeping context - I'll fix that.

The number of retries is just to bound the loop due to its inherent 
raciness - since we drop the lock to create more entries, under 
pathological conditions by the time we get back in to grab one they 
could have all gone. 2 retries (well, strictly it's 1 try and 1 retry) 
was an entirely arbitrary choice just to accommodate that happening very 
occasionally by chance.

However, if the dynamic allocations need GFP_ATOMIC for external reasons 
anyway, then I don't need the lock-juggling that invites that race in 
the first place, and the whole loop disappears again. Neat!

Robin.

Re: [PATCH 3/4] dma-debug: Dynamically expand the dma_debug_entry pool

[Robin Murphy]

On 04/12/2018 14:29, Christoph Hellwig wrote:
>> +	for (retry_count = 0; ; retry_count++) {
>> +		spin_lock_irqsave(&free_entries_lock, flags);
>> +
>> +		if (num_free_entries > 0)
>> +			break;
>>   
>>   		spin_unlock_irqrestore(&free_entries_lock, flags);
> 
> Taking a spinlock just to read a single integer value doesn't really
> help anything.

If the freelist is non-empty we break out with the lock still held in 
order to actually allocate our entry - only if there are no free entries 
left do we drop the lock in order to handle the failure. This much is 
just the original logic shuffled around a bit (with the tweak that 
testing num_free_entries seemed justifiably simpler than the original 
list_empty() check).

>> +
>> +		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
>> +		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
> 
> Don't we need GFP_ATOMIC here?  Also why do we need the retries?

Ah, right, we may be outside our own spinlock, but of course the whole 
DMA API call which got us here might be under someone else's and/or in a 
non-sleeping context - I'll fix that.

The number of retries is just to bound the loop due to its inherent 
raciness - since we drop the lock to create more entries, under 
pathological conditions by the time we get back in to grab one they 
could have all gone. 2 retries (well, strictly it's 1 try and 1 retry) 
was an entirely arbitrary choice just to accommodate that happening very 
occasionally by chance.

However, if the dynamic allocations need GFP_ATOMIC for external reasons 
anyway, then I don't need the lock-juggling that invites that race in 
the first place, and the whole loop disappears again. Neat!

Robin.

[RFC 4/4] dma-debug: Make leak-like behaviour apparent

[Robin Murphy]

Now that we can dynamically allocate DMA debug entries to cope with
drivers maintaining excessively large numbers of live mappings, a driver
which *does* actually have a bug leaking mappings (and is not unloaded)
will no longer trigger the "DMA-API: debugging out of memory - disabling"
message until it gets to actual kernel OOM conditions, which means it
could go unnoticed for a while. To that end, let's inform the user each
time the pool has grown to a multiple of its initial size, which should
make it apparent that they either have a leak or might want to increase
the preallocation size.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

Tagging this one as RFC since people might think it's silly.

 kernel/dma/debug.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 46cc075aec99..c4759dab0f8c 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -696,6 +696,17 @@ static struct dma_debug_entry *__dma_entry_alloc(void)
 	return entry;
 }
 
+void __dma_entry_alloc_check_leak(void)
+{
+	u32 tmp = nr_total_entries % nr_prealloc_entries;
+
+	/* Shout each time we tick over some multiple of the initial pool */
+	if (tmp < DMA_DEBUG_DYNAMIC_ENTRIES) {
+		pr_info("dma_debug_entry pool grown to %u00%% - possible mapping leak?\n",
+			(nr_total_entries / nr_prealloc_entries));
+	}
+}
+
 /* struct dma_entry allocator
  *
  * The next two functions implement the allocator for
@@ -716,8 +727,10 @@ static struct dma_debug_entry *dma_entry_alloc(void)
 		spin_unlock_irqrestore(&free_entries_lock, flags);
 
 		if (retry_count < DMA_DEBUG_DYNAMIC_RETRIES &&
-		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES))
+		    !prealloc_memory(DMA_DEBUG_DYNAMIC_ENTRIES)) {
+			__dma_entry_alloc_check_leak();
 			continue;
+		}
 
 		global_disable = true;
 		pr_err("debugging out of memory - disabling\n");
-- 
2.19.1.dirty

Re: [RFC 4/4] dma-debug: Make leak-like behaviour apparent

[Christoph Hellwig]

On Mon, Dec 03, 2018 at 05:28:09PM +0000, Robin Murphy wrote:
> Now that we can dynamically allocate DMA debug entries to cope with
> drivers maintaining excessively large numbers of live mappings, a driver
> which *does* actually have a bug leaking mappings (and is not unloaded)
> will no longer trigger the "DMA-API: debugging out of memory - disabling"
> message until it gets to actual kernel OOM conditions, which means it
> could go unnoticed for a while. To that end, let's inform the user each
> time the pool has grown to a multiple of its initial size, which should
> make it apparent that they either have a leak or might want to increase
> the preallocation size.
> 
> Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
> ---
> 
> Tagging this one as RFC since people might think it's silly.

I think finding out the numbers is useful, but I'm a little worried
about claiming a possible leak.  Maybe we just need to print a log message
for each new power of 2 of entries reached?

Re: [RFC 4/4] dma-debug: Make leak-like behaviour apparent

[Christoph Hellwig]

On Mon, Dec 03, 2018 at 05:28:09PM +0000, Robin Murphy wrote:
> Now that we can dynamically allocate DMA debug entries to cope with
> drivers maintaining excessively large numbers of live mappings, a driver
> which *does* actually have a bug leaking mappings (and is not unloaded)
> will no longer trigger the "DMA-API: debugging out of memory - disabling"
> message until it gets to actual kernel OOM conditions, which means it
> could go unnoticed for a while. To that end, let's inform the user each
> time the pool has grown to a multiple of its initial size, which should
> make it apparent that they either have a leak or might want to increase
> the preallocation size.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> 
> Tagging this one as RFC since people might think it's silly.

I think finding out the numbers is useful, but I'm a little worried
about claiming a possible leak.  Maybe we just need to print a log message
for each new power of 2 of entries reached?

Re: [PATCH 0/4] dma-debug: implement dynamic entry allocation

[Christoph Hellwig]

On Mon, Dec 03, 2018 at 05:28:05PM +0000, Robin Murphy wrote:
> The HNS_ENET discussion got me thinking, why not just make DMA debug
> cleverer so that (in terms of basic functionality at least) we don't
> need to worry about driver- or arch-specific configuration at all?
> 
> Patches #2 and #3 are the real meat here - #1 is just some preparatory
> cleanup motivated by moving printks around, and could be split out if
> desired; I kept #4 separate as a possible nice-to-have depending on
> what people think.

Hah, I just thought of this and suggested it a few seconds ago.
So obviously I think it is a good idea, but let me look at the details.