linux-kernel - [PATCH 1/1] mm/page_owner: fix recursion bug after changing skip entries

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Date:   Wed, 21 Mar 2018 10:07:23 +0530
From:   Maninder Singh <maninder1.s@...sung.com>
To:     akpm@...ux-foundation.org, vbabka@...e.cz, mhocko@...e.com,
        osalvador@...hadventures.net, gregkh@...uxfoundation.org,
        ayush.m@...sung.com, guptap@...eaurora.org,
        vinmenon@...eaurora.org, gomonovych@...il.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        a.sahrawat@...sung.com, pankaj.m@...sung.com,
        Maninder Singh <maninder1.s@...sung.com>,
        Vaneet Narang <v.narang@...sung.com>
Subject: [PATCH 1/1] mm/page_owner: fix recursion bug after changing skip
 entries

This patch fixes "5f48f0bd4e368425db4424b9afd1bd251d32367a".
(mm, page_owner: skip unnecessary stack_trace entries)

Because if we skip first two entries then logic of checking count
value as 2 for recursion is broken and code will go in one depth
recursion.

so we need to check only one call of _RET_IP(__set_page_owner)
while checking for recursion.

Current Backtrace while checking for recursion:-

(save_stack)             from (__set_page_owner)  // (But recursion returns true here)
(__set_page_owner)       from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack)       from (save_stack)       // recursion should return true here
(save_stack)             from (__set_page_owner)
(__set_page_owner)       from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask+)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack)       from (save_stack)
(save_stack)             from (__set_page_owner)
(__set_page_owner)       from (get_page_from_freelist)

Correct Backtrace with fix:

(save_stack)             from (__set_page_owner) // recursion returned true here
(__set_page_owner)       from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask+)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack)       from (save_stack)
(save_stack)             from (__set_page_owner)
(__set_page_owner)       from (get_page_from_freelist)

Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
Signed-off-by: Vaneet Narang <v.narang@...sung.com>
---
 mm/page_owner.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 8592543..46ab1c4 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -123,13 +123,13 @@ void __reset_page_owner(struct page *page, unsigned int order)
 static inline bool check_recursive_alloc(struct stack_trace *trace,
 					unsigned long ip)
 {
-	int i, count;
+	int i;
 
 	if (!trace->nr_entries)
 		return false;
 
-	for (i = 0, count = 0; i < trace->nr_entries; i++) {
-		if (trace->entries[i] == ip && ++count == 2)
+	for (i = 0; i < trace->nr_entries; i++) {
+		if (trace->entries[i] == ip)
 			return true;
 	}
 
-- 
1.7.1