mm: print more details for bad_page()

bad_page() is cool in that it prints out a bunch of data about the page.
But, I can never remember which page flags are good and which are bad,
or whether ->index or ->mapping is required to be NULL.

This patch allows bad/dump_page() callers to specify a string about why
they are dumping the page and adds explanation strings to a number of
places.  It also adds a 'bad_flags' argument to bad_page(), which it
then dumps out separately from the flags which are actually set.

This way, the messages will show specifically why the page was bad,
*specifically* which flags it is complaining about, if it was a page
flag combination which was the problem.

[akpm@linux-foundation.org: switch to pr_alert]
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Christoph Lameter <cl@linux.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 54 insertions, 18 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 533e214..1939f44 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -295,7 +295,7 @@ static inline int bad_range(struct zone *zone, struct page *page)
 }
 #endif
 
-static void bad_page(struct page *page)
+static void bad_page(struct page *page, char *reason, unsigned long bad_flags)
 {
 	static unsigned long resume;
 	static unsigned long nr_shown;
@@ -329,7 +329,7 @@ static void bad_page(struct page *page)
 
 	printk(KERN_ALERT "BUG: Bad page state in process %s  pfn:%05lx\n",
 		current->comm, page_to_pfn(page));
-	dump_page(page);
+	dump_page_badflags(page, reason, bad_flags);
 
 	print_modules();
 	dump_stack();
@@ -383,7 +383,7 @@ static int destroy_compound_page(struct page *page, unsigned long order)
 	int bad = 0;
 
 	if (unlikely(compound_order(page) != order)) {
-		bad_page(page);
+		bad_page(page, "wrong compound order", 0);
 		bad++;
 	}
 
@@ -392,8 +392,11 @@ static int destroy_compound_page(struct page *page, unsigned long order)
 	for (i = 1; i < nr_pages; i++) {
 		struct page *p = page + i;
 
-		if (unlikely(!PageTail(p) || (p->first_page != page))) {
-			bad_page(page);
+		if (unlikely(!PageTail(p))) {
+			bad_page(page, "PageTail not set", 0);
+			bad++;
+		} else if (unlikely(p->first_page != page)) {
+			bad_page(page, "first_page not consistent", 0);
 			bad++;
 		}
 		__ClearPageTail(p);
@@ -618,12 +621,23 @@ out:
 
 static inline int free_pages_check(struct page *page)
 {
-	if (unlikely(page_mapcount(page) |
-		(page->mapping != NULL)  |
-		(atomic_read(&page->_count) != 0) |
-		(page->flags & PAGE_FLAGS_CHECK_AT_FREE) |
-		(mem_cgroup_bad_page_check(page)))) {
-		bad_page(page);
+	char *bad_reason = NULL;
+	unsigned long bad_flags = 0;
+
+	if (unlikely(page_mapcount(page)))
+		bad_reason = "nonzero mapcount";
+	if (unlikely(page->mapping != NULL))
+		bad_reason = "non-NULL mapping";
+	if (unlikely(atomic_read(&page->_count) != 0))
+		bad_reason = "nonzero _count";
+	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
+		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
+		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
+	}
+	if (unlikely(mem_cgroup_bad_page_check(page)))
+		bad_reason = "cgroup check failed";
+	if (unlikely(bad_reason)) {
+		bad_page(page, bad_reason, bad_flags);
 		return 1;
 	}
 	page_cpupid_reset_last(page);
@@ -843,12 +857,23 @@ static inline void expand(struct zone *zone, struct page *page,
  */
 static inline int check_new_page(struct page *page)
 {
-	if (unlikely(page_mapcount(page) |
-		(page->mapping != NULL)  |
-		(atomic_read(&page->_count) != 0)  |
-		(page->flags & PAGE_FLAGS_CHECK_AT_PREP) |
-		(mem_cgroup_bad_page_check(page)))) {
-		bad_page(page);
+	char *bad_reason = NULL;
+	unsigned long bad_flags = 0;
+
+	if (unlikely(page_mapcount(page)))
+		bad_reason = "nonzero mapcount";
+	if (unlikely(page->mapping != NULL))
+		bad_reason = "non-NULL mapping";
+	if (unlikely(atomic_read(&page->_count) != 0))
+		bad_reason = "nonzero _count";
+	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
+		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
+		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
+	}
+	if (unlikely(mem_cgroup_bad_page_check(page)))
+		bad_reason = "cgroup check failed";
+	if (unlikely(bad_reason)) {
+		bad_page(page, bad_reason, bad_flags);
 		return 1;
 	}
 	return 0;
@@ -6494,12 +6519,23 @@ static void dump_page_flags(unsigned long flags)
 	printk(")\n");
 }
 
-void dump_page(struct page *page)
+void dump_page_badflags(struct page *page, char *reason, unsigned long badflags)
 {
 	printk(KERN_ALERT
 	       "page:%p count:%d mapcount:%d mapping:%p index:%#lx\n",
 		page, atomic_read(&page->_count), page_mapcount(page),
 		page->mapping, page->index);
 	dump_page_flags(page->flags);
+	if (reason)
+		pr_alert("page dumped because: %s\n", reason);
+	if (page->flags & badflags) {
+		pr_alert("bad because of flags:\n");
+		dump_page_flags(page->flags & badflags);
+	}
 	mem_cgroup_print_bad_page(page);
 }
+
+void dump_page(struct page *page, char *reason)
+{
+	dump_page_badflags(page, reason, 0);
+}