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From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Al Viro" <viro@zeniv.linux.org.uk>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Dave Chinner" <david@fromorbit.com>,
	"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Matthew Wilcox" <willy@infradead.org>,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH v6 11/12] mm: Improve dump_page() for compound pages
Date: Mon, 10 Feb 2020 16:15:35 -0800
Message-ID: <20200211001536.1027652-12-jhubbard@nvidia.com> (raw)
In-Reply-To: <20200211001536.1027652-1-jhubbard@nvidia.com>

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

There was no protection against a corrupted struct page having an
implausible compound_head().  Sanity check that a compound page has
a head within reach of the maximum allocatable page (this will need
to be adjusted if one of the plans to allocate 1GB pages comes to
fruition).  In addition,

 - Print the mapping pointer using %p insted of %px.  The actual value of
   the pointer can be read out of the raw page dump and using %p gives a
   chance to correlate it with an earlier printk of the mapping pointer
 - Print the mapping pointer from the head page, not the tail page
   (the tail ->mapping pointer may be in use for other purposes, eg part
   of a list_head)
 - Print the order of the page for compound pages
 - Dump the raw head page as well as the raw page
 - Print the refcount from the head page, not the tail page

Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Co-developed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/debug.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/mm/debug.c b/mm/debug.c
index ecccd9f17801..f5ffb0784559 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -44,8 +44,10 @@ const struct trace_print_flags vmaflag_names[] = {
 
 void __dump_page(struct page *page, const char *reason)
 {
+	struct page *head = compound_head(page);
 	struct address_space *mapping;
 	bool page_poisoned = PagePoisoned(page);
+	bool compound = PageCompound(page);
 	/*
 	 * Accessing the pageblock without the zone lock. It could change to
 	 * "isolate" again in the meantime, but since we are just dumping the
@@ -66,25 +68,32 @@ void __dump_page(struct page *page, const char *reason)
 		goto hex_only;
 	}
 
-	mapping = page_mapping(page);
+	if (page < head || (page >= head + MAX_ORDER_NR_PAGES)) {
+		/* Corrupt page, cannot call page_mapping */
+		mapping = page->mapping;
+		head = page;
+		compound = false;
+	} else {
+		mapping = page_mapping(page);
+	}
 
 	/*
 	 * Avoid VM_BUG_ON() in page_mapcount().
 	 * page->_mapcount space in struct page is used by sl[aou]b pages to
 	 * encode own info.
 	 */
-	mapcount = PageSlab(page) ? 0 : page_mapcount(page);
+	mapcount = PageSlab(head) ? 0 : page_mapcount(page);
 
-	if (PageCompound(page))
-		pr_warn("page:%px refcount:%d mapcount:%d mapping:%px "
-			"index:%#lx compound_mapcount: %d\n",
-			page, page_ref_count(page), mapcount,
-			page->mapping, page_to_pgoff(page),
-			compound_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));
 	else
-		pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
+		pr_warn("page:%px refcount:%d mapcount:%d mapping:%p index:%#lx\n",
 			page, page_ref_count(page), mapcount,
-			page->mapping, page_to_pgoff(page));
+			mapping, page_to_pgoff(page));
 	if (PageKsm(page))
 		type = "ksm ";
 	else if (PageAnon(page))
@@ -106,6 +115,10 @@ void __dump_page(struct page *page, const char *reason)
 	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
 			sizeof(unsigned long), page,
 			sizeof(struct page), false);
+	if (head != page)
+		print_hex_dump(KERN_WARNING, "head: ", DUMP_PREFIX_NONE, 32,
+			sizeof(unsigned long), head,
+			sizeof(struct page), false);
 
 	if (reason)
 		pr_warn("page dumped because: %s\n", reason);
-- 
2.25.0


  parent reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11  0:15 [PATCH v6 00/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-11  0:15 ` [PATCH v6 01/12] mm/gup: split get_user_pages_remote() into two routines John Hubbard
2020-02-11  0:15 ` [PATCH v6 02/12] mm/gup: pass a flags arg to __gup_device_* functions John Hubbard
2020-02-11  0:15 ` [PATCH v6 03/12] mm: introduce page_ref_sub_return() John Hubbard
2020-02-11  0:15 ` [PATCH v6 04/12] mm/gup: pass gup flags to two more routines John Hubbard
2020-02-11  0:15 ` [PATCH v6 05/12] mm/gup: require FOLL_GET for get_user_pages_fast() John Hubbard
2020-02-11  0:15 ` [PATCH v6 06/12] mm/gup: track FOLL_PIN pages John Hubbard
2020-02-11  0:15 ` [PATCH v6 07/12] mm/gup: page->hpage_pinned_refcount: exact pin counts for huge pages John Hubbard
2020-02-11  0:15 ` [PATCH v6 08/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting John Hubbard
2020-02-12  9:17   ` Jan Kara
2020-02-11  0:15 ` [PATCH v6 09/12] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2020-02-11  0:15 ` [PATCH v6 10/12] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2020-02-11  0:15 ` John Hubbard [this message]
2020-02-11  0:15 ` [PATCH v6 12/12] mm: dump_page(): additional diagnostics for huge pinned pages John Hubbard
2020-02-11 13:21   ` Kirill A. Shutemov
2020-02-12  2:10     ` John Hubbard

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