[PATCH net-next 2/2] net/sctp: Replace in/out stream arrays with flex_array

[Oleg Babin <obabin@virtuozzo.com>]

This path replaces physically contiguous memory arrays
allocated using kmalloc_array() with flexible arrays.
This enables to avoid memory allocation failures on the
systems under a memory stress.

Signed-off-by: Oleg Babin <obabin@virtuozzo.com>
---
 include/net/sctp/structs.h |  1 +
 net/sctp/stream.c          | 78 +++++++++++++++++++++++++++++++++++-----------
 2 files changed, 61 insertions(+), 18 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 578bb40..c7f42b4 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -57,6 +57,7 @@
 #include <linux/atomic.h>		/* This gets us atomic counters.  */
 #include <linux/skbuff.h>	/* We need sk_buff_head. */
 #include <linux/workqueue.h>	/* We need tq_struct.	 */
+#include <linux/flex_array.h>	/* We need flex_array.   */
 #include <linux/sctp.h>		/* We need sctp* header structs.  */
 #include <net/sctp/auth.h>	/* We need auth specific structs */
 #include <net/ip.h>		/* For inet_skb_parm */
diff --git a/net/sctp/stream.c b/net/sctp/stream.c
index 16e36c0..be372b0 100644
--- a/net/sctp/stream.c
+++ b/net/sctp/stream.c
@@ -40,13 +40,60 @@
 struct sctp_stream_out *sctp_stream_out_ptr(const struct sctp_stream *stream,
 					    __u16 sid)
 {
-	return ((struct sctp_stream_out *)(stream->out)) + sid;
+	return flex_array_get(stream->out, sid);
 }
 
 struct sctp_stream_in *sctp_stream_in_ptr(const struct sctp_stream *stream,
 					  __u16 sid)
 {
-	return ((struct sctp_stream_in *)(stream->in)) + sid;
+	return flex_array_get(stream->in, sid);
+}
+
+static struct flex_array *fa_alloc(size_t elem_size, size_t elem_count,
+				   gfp_t gfp)
+{
+	struct flex_array *result;
+	int err;
+
+	result = flex_array_alloc(elem_size, elem_count, gfp);
+	if (result) {
+		err = flex_array_prealloc(result, 0, elem_count, gfp);
+		if (err) {
+			flex_array_free(result);
+			result = NULL;
+		}
+	}
+
+	return result;
+}
+
+static void fa_free(struct flex_array *fa)
+{
+	if (fa)
+		flex_array_free(fa);
+}
+
+static void fa_copy(struct flex_array *fa, struct flex_array *from,
+		    size_t index, size_t count)
+{
+	void *elem;
+
+	while (count--) {
+		elem = flex_array_get(from, index);
+		flex_array_put(fa, index, elem, 0);
+		index++;
+	}
+}
+
+static void fa_zero(struct flex_array *fa, size_t index, size_t count)
+{
+	void *elem;
+
+	while (count--) {
+		elem = flex_array_get(fa, index);
+		memset(elem, 0, fa->element_size);
+		index++;
+	}
 }
 
 /* Migrates chunks from stream queues to new stream queues if needed,
@@ -106,19 +153,17 @@ static int sctp_stream_alloc_out(struct sctp_stream *stream, __u16 outcnt,
 	struct flex_array *out;
 	size_t elem_size = sizeof(struct sctp_stream_out);
 
-	out = kmalloc_array(outcnt, elem_size, gfp);
+	out = fa_alloc(elem_size, outcnt, gfp);
 	if (!out)
 		return -ENOMEM;
 
 	if (stream->out) {
-		memcpy(out, stream->out, min(outcnt, stream->outcnt) *
-					 elem_size);
-		kfree(stream->out);
+		fa_copy(out, stream->out, 0, min(outcnt, stream->outcnt));
+		fa_free(stream->out);
 	}
 
 	if (outcnt > stream->outcnt)
-		memset(((struct sctp_stream_out *)out) + stream->outcnt, 0,
-		       (outcnt - stream->outcnt) * elem_size);
+		fa_zero(out, stream->outcnt, (outcnt - stream->outcnt));
 
 	stream->out = out;
 
@@ -131,20 +176,17 @@ static int sctp_stream_alloc_in(struct sctp_stream *stream, __u16 incnt,
 	struct flex_array *in;
 	size_t elem_size = sizeof(struct sctp_stream_in);
 
-	in = kmalloc_array(incnt, elem_size, gfp);
-
+	in = fa_alloc(elem_size, incnt, gfp);
 	if (!in)
 		return -ENOMEM;
 
 	if (stream->in) {
-		memcpy(in, stream->in, min(incnt, stream->incnt) *
-				       elem_size);
-		kfree(stream->in);
+		fa_copy(in, stream->in, 0, min(incnt, stream->incnt));
+		fa_free(stream->in);
 	}
 
 	if (incnt > stream->incnt)
-		memset(((struct sctp_stream_in *)in) + stream->incnt, 0,
-		       (incnt - stream->incnt) * elem_size);
+		fa_zero(in, stream->incnt, (incnt - stream->incnt));
 
 	stream->in = in;
 
@@ -188,7 +230,7 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
 	ret = sctp_stream_alloc_in(stream, incnt, gfp);
 	if (ret) {
 		sched->free(stream);
-		kfree(stream->out);
+		fa_free(stream->out);
 		stream->out = NULL;
 		stream->outcnt = 0;
 		goto out;
@@ -220,8 +262,8 @@ void sctp_stream_free(struct sctp_stream *stream)
 	sched->free(stream);
 	for (i = 0; i < stream->outcnt; i++)
 		kfree(SCTP_SO(stream, i)->ext);
-	kfree(stream->out);
-	kfree(stream->in);
+	fa_free(stream->out);
+	fa_free(stream->in);
 }
 
 void sctp_stream_clear(struct sctp_stream *stream)
-- 
1.8.3.1