[PATCHv2] tracing: simplify pages allocation

[Rosen Penev <rosenp@gmail.com>]

Change to a flexible array member to allocate together with the array
struct.

Simplifies code slightly by removing no longer correct null checks for
pages and removing kfrees.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v2: add back kfree(a). Accidentally removed.
 kernel/trace/tracing_map.c | 30 +++++++++++-------------------
 kernel/trace/tracing_map.h |  2 +-
 2 files changed, 12 insertions(+), 20 deletions(-)

diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
index c59326ad7a84..97f7e3cde262 100644
--- a/kernel/trace/tracing_map.c
+++ b/kernel/trace/tracing_map.c
@@ -288,9 +288,6 @@ static void tracing_map_array_clear(struct tracing_map_array *a)
 {
 	unsigned int i;

-	if (!a->pages)
-		return;
-
 	for (i = 0; i < a->n_pages; i++)
 		memset(a->pages[i], 0, PAGE_SIZE);
 }
@@ -302,9 +299,6 @@ static void tracing_map_array_free(struct tracing_map_array *a)
 	if (!a)
 		return;

-	if (!a->pages)
-		goto free;
-
 	for (i = 0; i < a->n_pages; i++) {
 		if (!a->pages[i])
 			break;
@@ -312,9 +306,6 @@ static void tracing_map_array_free(struct tracing_map_array *a)
 		free_page((unsigned long)a->pages[i]);
 	}

-	kfree(a->pages);
-
- free:
 	kfree(a);
 }

@@ -322,24 +313,25 @@ static struct tracing_map_array *tracing_map_array_alloc(unsigned int n_elts,
 						  unsigned int entry_size)
 {
 	struct tracing_map_array *a;
+	unsigned int entry_size_shift;
+	unsigned int entries_per_page;
+	unsigned int n_pages;
 	unsigned int i;

-	a = kzalloc_obj(*a);
+	entry_size_shift = fls(roundup_pow_of_two(entry_size) - 1);
+	entries_per_page = PAGE_SIZE / (1 << entry_size_shift);
+	n_pages = max(1, n_elts / entries_per_page);
+
+	a = kzalloc_flex(*a, pages, n_pages);
 	if (!a)
 		return NULL;

-	a->entry_size_shift = fls(roundup_pow_of_two(entry_size) - 1);
-	a->entries_per_page = PAGE_SIZE / (1 << a->entry_size_shift);
-	a->n_pages = n_elts / a->entries_per_page;
-	if (!a->n_pages)
-		a->n_pages = 1;
+	a->entry_size_shift = entry_size_shift;
+	a->entries_per_page = entries_per_page;
+	a->n_pages = n_pages;
 	a->entry_shift = fls(a->entries_per_page) - 1;
 	a->entry_mask = (1 << a->entry_shift) - 1;

-	a->pages = kcalloc(a->n_pages, sizeof(void *), GFP_KERNEL);
-	if (!a->pages)
-		goto free;
-
 	for (i = 0; i < a->n_pages; i++) {
 		a->pages[i] = (void *)get_zeroed_page(GFP_KERNEL);
 		if (!a->pages[i])
diff --git a/kernel/trace/tracing_map.h b/kernel/trace/tracing_map.h
index ed64136782d8..90a7fde5dd02 100644
--- a/kernel/trace/tracing_map.h
+++ b/kernel/trace/tracing_map.h
@@ -167,7 +167,7 @@ struct tracing_map_array {
 	unsigned int entry_shift;
 	unsigned int entry_mask;
 	unsigned int n_pages;
-	void **pages;
+	void *pages[] __counted_by(n_pages);
 };

 #define TRACING_MAP_ARRAY_ELT(array, idx)				\
--
2.54.0