ALSA: pcm: Set per-card upper limit of PCM buffer allocations

Currently, the available buffer allocation size for a PCM stream
depends on the preallocated size; when a buffer has been preallocated,
the max buffer size is set to that size, so that application won't
re-allocate too much memory.  OTOH, when no preallocation is done,
each substream may allocate arbitrary size of buffers as long as
snd_pcm_hardware.buffer_bytes_max allows -- which can be quite high,
HD-audio sets 1GB there.

It means that the system may consume a high amount of pages for PCM
buffers, and they are pinned and never swapped out.  This can lead to
OOM easily.

For avoiding such a situation, this patch adds the upper limit per
card.  Each snd_pcm_lib_malloc_pages() and _free_pages() calls are
tracked and it will return an error if the total amount of buffers
goes over the defined upper limit.  The default value is set to 32MB,
which should be really large enough for usual operations.

If larger buffers are needed for any specific usage, it can be
adjusted (also dynamically) via snd_pcm.max_alloc_per_card option.
Setting zero there means no chceck is performed, and again, unlimited
amount of buffers are allowed.

Link: https://lore.kernel.org/r/20200120124423.11862-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 51 insertions, 18 deletions

diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c
index d4702cc1d376..fcab37ea6641 100644
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -27,6 +27,38 @@ MODULE_PARM_DESC(maximum_substreams, "Maximum substreams with preallocated DMA m
 
 static const size_t snd_minimum_buffer = 16384;
 
+static unsigned long max_alloc_per_card = 32UL * 1024UL * 1024UL;
+module_param(max_alloc_per_card, ulong, 0644);
+MODULE_PARM_DESC(max_alloc_per_card, "Max total allocation bytes per card.");
+
+static int do_alloc_pages(struct snd_card *card, int type, struct device *dev,
+			  size_t size, struct snd_dma_buffer *dmab)
+{
+	int err;
+
+	if (max_alloc_per_card &&
+	    card->total_pcm_alloc_bytes + size > max_alloc_per_card)
+		return -ENOMEM;
+	err = snd_dma_alloc_pages(type, dev, size, dmab);
+	if (!err) {
+		mutex_lock(&card->memory_mutex);
+		card->total_pcm_alloc_bytes += dmab->bytes;
+		mutex_unlock(&card->memory_mutex);
+	}
+	return err;
+}
+
+static void do_free_pages(struct snd_card *card, struct snd_dma_buffer *dmab)
+{
+	if (!dmab->area)
+		return;
+	mutex_lock(&card->memory_mutex);
+	WARN_ON(card->total_pcm_alloc_bytes < dmab->bytes);
+	card->total_pcm_alloc_bytes -= dmab->bytes;
+	mutex_unlock(&card->memory_mutex);
+	snd_dma_free_pages(dmab);
+	dmab->area = NULL;
+}
 
 /*
  * try to allocate as the large pages as possible.
@@ -37,16 +69,15 @@ static const size_t snd_minimum_buffer = 16384;
 static int preallocate_pcm_pages(struct snd_pcm_substream *substream, size_t size)
 {
 	struct snd_dma_buffer *dmab = &substream->dma_buffer;
+	struct snd_card *card = substream->pcm->card;
 	size_t orig_size = size;
 	int err;
 
 	do {
-		if ((err = snd_dma_alloc_pages(dmab->dev.type, dmab->dev.dev,
-					       size, dmab)) < 0) {
-			if (err != -ENOMEM)
-				return err; /* fatal error */
-		} else
-			return 0;
+		err = do_alloc_pages(card, dmab->dev.type, dmab->dev.dev,
+				     size, dmab);
+		if (err != -ENOMEM)
+			return err;
 		size >>= 1;
 	} while (size >= snd_minimum_buffer);
 	dmab->bytes = 0; /* tell error */
@@ -62,10 +93,7 @@ static int preallocate_pcm_pages(struct snd_pcm_substream *substream, size_t siz
  */
 static void snd_pcm_lib_preallocate_dma_free(struct snd_pcm_substream *substream)
 {
-	if (substream->dma_buffer.area == NULL)
-		return;
-	snd_dma_free_pages(&substream->dma_buffer);
-	substream->dma_buffer.area = NULL;
+	do_free_pages(substream->pcm->card, &substream->dma_buffer);
 }
 
 /**
@@ -130,6 +158,7 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
 					       struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
+	struct snd_card *card = substream->pcm->card;
 	char line[64], str[64];
 	size_t size;
 	struct snd_dma_buffer new_dmab;
@@ -150,9 +179,10 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
 		memset(&new_dmab, 0, sizeof(new_dmab));
 		new_dmab.dev = substream->dma_buffer.dev;
 		if (size > 0) {
-			if (snd_dma_alloc_pages(substream->dma_buffer.dev.type,
-						substream->dma_buffer.dev.dev,
-						size, &new_dmab) < 0) {
+			if (do_alloc_pages(card,
+					   substream->dma_buffer.dev.type,
+					   substream->dma_buffer.dev.dev,
+					   size, &new_dmab) < 0) {
 				buffer->error = -ENOMEM;
 				return;
 			}
@@ -161,7 +191,7 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
 			substream->buffer_bytes_max = UINT_MAX;
 		}
 		if (substream->dma_buffer.area)
-			snd_dma_free_pages(&substream->dma_buffer);
+			do_free_pages(card, &substream->dma_buffer);
 		substream->dma_buffer = new_dmab;
 	} else {
 		buffer->error = -EINVAL;
@@ -346,6 +376,7 @@ struct page *snd_pcm_sgbuf_ops_page(struct snd_pcm_substream *substream, unsigne
  */
 int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
 {
+	struct snd_card *card = substream->pcm->card;
 	struct snd_pcm_runtime *runtime;
 	struct snd_dma_buffer *dmab = NULL;
 
@@ -374,9 +405,10 @@ int snd_pcm_lib_malloc_pages(struct snd_pcm_substream *substream, size_t size)
 		if (! dmab)
 			return -ENOMEM;
 		dmab->dev = substream->dma_buffer.dev;
-		if (snd_dma_alloc_pages(substream->dma_buffer.dev.type,
-					substream->dma_buffer.dev.dev,
-					size, dmab) < 0) {
+		if (do_alloc_pages(card,
+				   substream->dma_buffer.dev.type,
+				   substream->dma_buffer.dev.dev,
+				   size, dmab) < 0) {
 			kfree(dmab);
 			return -ENOMEM;
 		}
@@ -397,6 +429,7 @@ EXPORT_SYMBOL(snd_pcm_lib_malloc_pages);
  */
 int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream)
 {
+	struct snd_card *card = substream->pcm->card;
 	struct snd_pcm_runtime *runtime;
 
 	if (PCM_RUNTIME_CHECK(substream))
@@ -406,7 +439,7 @@ int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream)
 		return 0;
 	if (runtime->dma_buffer_p != &substream->dma_buffer) {
 		/* it's a newly allocated buffer.  release it now. */
-		snd_dma_free_pages(runtime->dma_buffer_p);
+		do_free_pages(card, runtime->dma_buffer_p);
 		kfree(runtime->dma_buffer_p);
 	}
 	snd_pcm_set_runtime_buffer(substream, NULL);