Commit 4d35427a authored Sep 19, 2016 by Kirill A. Shutemov Committed by Linus Torvalds Sep 19, 2016

mm: avoid endless recursion in dump_page()

dump_page() uses page_mapcount() to get mapcount of the page.
page_mapcount() has VM_BUG_ON_PAGE(PageSlab(page)) as mapcount doesn't
make sense for slab pages and the field in struct page used for other
information.

It leads to recursion if dump_page() called for slub page and DEBUG_VM
is enabled:

dump_page() -> page_mapcount() -> VM_BUG_ON_PAGE() -> dump_page -> ...

Let's avoid calling page_mapcount() for slab pages in dump_page().

Link: http://lkml.kernel.org/r/20160908082137.131076-1-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 982785c6

mm/debug.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -42,9 +42,11 @@ const struct trace_print_flags vmaflag_names[] = {

		void __dump_page(struct page page, const char reason)
		{
		int mapcount = PageSlab(page) ? 0 : page_mapcount(page);

		pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
		page, page_ref_count(page), page_mapcount(page),
		page->mapping, page->index);
		page, page_ref_count(page), mapcount,
		page->mapping, page_to_pgoff(page));
		if (PageCompound(page))
		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
		pr_cont("\n");

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