linux-kernel - [PATCH 1/2] mm/page_owner: Introduce SNPRINTF() macro that includes length error check

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Date:   Fri, 28 Jan 2022 14:56:41 -0500
From:   Waiman Long <longman@...hat.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Rafael Aquini <aquini@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] mm/page_owner: Introduce SNPRINTF() macro that includes length error check

In print_page_owner(), there is a repetitive check after each snprintf()
to make sure that the final length is less than the buffer size. Simplify
the code and make it easier to read by embedding the buffer length
check and increment inside the macro.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 mm/page_owner.c | 50 +++++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 27 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 99e360df9465..c52ce9d6bc3b 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -325,12 +325,20 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 	seq_putc(m, '\n');
 }
 
+#define SNPRINTF(_buf, _size, _len, _err, _fmt, ...)			\
+	do {								\
+		_len += snprintf(_buf + _len, _size - _len, _fmt,	\
+				 ##__VA_ARGS__);			\
+		if (_len >= _size)					\
+			goto _err;					\
+	} while (0)
+
 static ssize_t
 print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 		struct page *page, struct page_owner *page_owner,
 		depot_stack_handle_t handle)
 {
-	int ret, pageblock_mt, page_mt;
+	int ret = 0, pageblock_mt, page_mt;
 	char *kbuf;
 
 	count = min_t(size_t, count, PAGE_SIZE);
@@ -338,44 +346,32 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 	if (!kbuf)
 		return -ENOMEM;
 
-	ret = snprintf(kbuf, count,
-			"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
-			page_owner->order, page_owner->gfp_mask,
-			&page_owner->gfp_mask, page_owner->pid,
-			page_owner->ts_nsec, page_owner->free_ts_nsec);
-
-	if (ret >= count)
-		goto err;
+	SNPRINTF(kbuf, count, ret, err,
+		"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
+		page_owner->order, page_owner->gfp_mask,
+		&page_owner->gfp_mask, page_owner->pid,
+		page_owner->ts_nsec, page_owner->free_ts_nsec);
 
 	/* Print information relevant to grouping pages by mobility */
 	pageblock_mt = get_pageblock_migratetype(page);
 	page_mt  = gfp_migratetype(page_owner->gfp_mask);
-	ret += snprintf(kbuf + ret, count - ret,
-			"PFN %lu type %s Block %lu type %s Flags %pGp\n",
-			pfn,
-			migratetype_names[page_mt],
-			pfn >> pageblock_order,
-			migratetype_names[pageblock_mt],
-			&page->flags);
-
-	if (ret >= count)
-		goto err;
+	SNPRINTF(kbuf, count, ret, err,
+		"PFN %lu type %s Block %lu type %s Flags %pGp\n",
+		pfn, migratetype_names[page_mt],
+		pfn >> pageblock_order,
+		migratetype_names[pageblock_mt],
+		&page->flags);
 
 	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
 	if (ret >= count)
 		goto err;
 
-	if (page_owner->last_migrate_reason != -1) {
-		ret += snprintf(kbuf + ret, count - ret,
+	if (page_owner->last_migrate_reason != -1)
+		SNPRINTF(kbuf, count, ret, err,
 			"Page has been migrated, last migrate reason: %s\n",
 			migrate_reason_names[page_owner->last_migrate_reason]);
-		if (ret >= count)
-			goto err;
-	}
 
-	ret += snprintf(kbuf + ret, count - ret, "\n");
-	if (ret >= count)
-		goto err;
+	SNPRINTF(kbuf, count, ret, err, "\n");
 
 	if (copy_to_user(buf, kbuf, ret))
 		ret = -EFAULT;
-- 
2.27.0