From dc8fb2f282ad13e550b65958fea40c7eb766d42a Mon Sep 17 00:00:00 2001
From: John Hubbard <jhubbard@nvidia.com>
Date: Wed, 1 Apr 2020 21:05:52 -0700
Subject: mm: dump_page(): additional diagnostics for huge pinned pages
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As part of pin_user_pages() and related API calls, pages are "dma-pinned".
For the case of compound pages of order > 1, the per-page accounting of
dma pins is accomplished via the 3rd struct page in the compound page.  In
order to support debugging of any pin_user_pages()- related problems,
enhance dump_page() so as to report the pin count in that case.

Documentation/core-api/pin_user_pages.rst is also updated accordingly.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/20200211001536.1027652-13-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/debug.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

(limited to 'mm/debug.c')

diff --git a/mm/debug.c b/mm/debug.c
index f5ffb0784559..2189357f0987 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -85,11 +85,22 @@ void __dump_page(struct page *page, const char *reason)
 	mapcount = PageSlab(head) ? 0 : page_mapcount(page);
 
 	if (compound)
-		pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
-			"index:%#lx head:%px order:%u compound_mapcount:%d\n",
-			page, page_ref_count(head), mapcount,
-			mapping, page_to_pgoff(page), head,
-			compound_order(head), compound_mapcount(page));
+		if (hpage_pincount_available(page)) {
+			pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
+				"index:%#lx head:%px order:%u "
+				"compound_mapcount:%d compound_pincount:%d\n",
+				page, page_ref_count(head), mapcount,
+				mapping, page_to_pgoff(page), head,
+				compound_order(head), compound_mapcount(page),
+				compound_pincount(page));
+		} else {
+			pr_warn("page:%px refcount:%d mapcount:%d mapping:%p "
+				"index:%#lx head:%px order:%u "
+				"compound_mapcount:%d\n",
+				page, page_ref_count(head), mapcount,
+				mapping, page_to_pgoff(page), head,
+				compound_order(head), compound_mapcount(page));
+		}
 	else
 		pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n",
 			page, page_ref_count(page), mapcount,
-- 
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