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Subject[RFC patch 26/41] mm/page_owner: Simplify stack trace handling
Replace the indirection through struct stack_trace by using the storage
array based interfaces.

The original code in all printing functions is really wrong. It allocates a
storage array on stack which is unused because depot_fetch_stack() does not
store anything in it. It overwrites the entries pointer in the stack_trace
struct so it points to the depot storage.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
mm/page_owner.c | 79 +++++++++++++++++++-------------------------------------
1 file changed, 28 insertions(+), 51 deletions(-)

--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -58,15 +58,10 @@ static bool need_page_owner(void)
static __always_inline depot_stack_handle_t create_dummy_stack(void)
{
unsigned long entries[4];
- struct stack_trace dummy;
+ unsigned int nent;

- dummy.nr_entries = 0;
- dummy.max_entries = ARRAY_SIZE(entries);
- dummy.entries = &entries[0];
- dummy.skip = 0;
-
- save_stack_trace(&dummy);
- return depot_save_stack(&dummy, GFP_KERNEL);
+ nent = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
+ return stack_depot_save(entries, nent, GFP_KERNEL);
}

static noinline void register_dummy_stack(void)
@@ -120,46 +115,39 @@ void __reset_page_owner(struct page *pag
}
}

-static inline bool check_recursive_alloc(struct stack_trace *trace,
- unsigned long ip)
+static inline bool check_recursive_alloc(unsigned long *entries,
+ unsigned int nr_entries,
+ unsigned long ip)
{
- int i;
+ unsigned int i;

- if (!trace->nr_entries)
- return false;
-
- for (i = 0; i < trace->nr_entries; i++) {
- if (trace->entries[i] == ip)
+ for (i = 0; i < nr_entries; i++) {
+ if (entries[i] == ip)
return true;
}
-
return false;
}

static noinline depot_stack_handle_t save_stack(gfp_t flags)
{
unsigned long entries[PAGE_OWNER_STACK_DEPTH];
- struct stack_trace trace = {
- .nr_entries = 0,
- .entries = entries,
- .max_entries = PAGE_OWNER_STACK_DEPTH,
- .skip = 2
- };
depot_stack_handle_t handle;
+ unsigned int nent;

- save_stack_trace(&trace);
+ nent = stack_trace_save(entries, ARRAY_SIZE(entries), 2);

/*
- * We need to check recursion here because our request to stackdepot
- * could trigger memory allocation to save new entry. New memory
- * allocation would reach here and call depot_save_stack() again
- * if we don't catch it. There is still not enough memory in stackdepot
- * so it would try to allocate memory again and loop forever.
+ * We need to check recursion here because our request to
+ * stackdepot could trigger memory allocation to save new
+ * entry. New memory allocation would reach here and call
+ * stack_depot_save_entries() again if we don't catch it. There is
+ * still not enough memory in stackdepot so it would try to
+ * allocate memory again and loop forever.
*/
- if (check_recursive_alloc(&trace, _RET_IP_))
+ if (check_recursive_alloc(entries, nent, _RET_IP_))
return dummy_handle;

- handle = depot_save_stack(&trace, flags);
+ handle = stack_depot_save(entries, nent, flags);
if (!handle)
handle = failure_handle;

@@ -337,16 +325,10 @@ print_page_owner(char __user *buf, size_
struct page *page, struct page_owner *page_owner,
depot_stack_handle_t handle)
{
- int ret;
- int pageblock_mt, page_mt;
+ int ret, pageblock_mt, page_mt;
+ unsigned long *entries;
+ unsigned int nent;
char *kbuf;
- unsigned long entries[PAGE_OWNER_STACK_DEPTH];
- struct stack_trace trace = {
- .nr_entries = 0,
- .entries = entries,
- .max_entries = PAGE_OWNER_STACK_DEPTH,
- .skip = 0
- };

count = min_t(size_t, count, PAGE_SIZE);
kbuf = kmalloc(count, GFP_KERNEL);
@@ -375,8 +357,8 @@ print_page_owner(char __user *buf, size_
if (ret >= count)
goto err;

- depot_fetch_stack(handle, &trace);
- ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
+ nent = stack_depot_fetch(handle, &entries);
+ ret += stack_trace_snprint(kbuf + ret, count - ret, entries, nent, 0);
if (ret >= count)
goto err;

@@ -407,14 +389,9 @@ void __dump_page_owner(struct page *page
{
struct page_ext *page_ext = lookup_page_ext(page);
struct page_owner *page_owner;
- unsigned long entries[PAGE_OWNER_STACK_DEPTH];
- struct stack_trace trace = {
- .nr_entries = 0,
- .entries = entries,
- .max_entries = PAGE_OWNER_STACK_DEPTH,
- .skip = 0
- };
depot_stack_handle_t handle;
+ unsigned long *entries;
+ unsigned int nent;
gfp_t gfp_mask;
int mt;

@@ -438,10 +415,10 @@ void __dump_page_owner(struct page *page
return;
}

- depot_fetch_stack(handle, &trace);
+ nent = stack_depot_fetch(handle, &entries);
pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
- print_stack_trace(&trace, 0);
+ stack_trace_print(entries, nent, 0);

if (page_owner->last_migrate_reason != -1)
pr_alert("page has been migrated, last migrate reason: %s\n",

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