Commit 6197ab98 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
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mm: improve dump_page() for compound pages

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

 - 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: default avatarKirill A. Shutemov <>
Co-developed-by: default avatarJohn Hubbard <>
Signed-off-by: default avatarMatthew Wilcox (Oracle) <>
Signed-off-by: default avatarJohn Hubbard <>
Signed-off-by: default avatarAndrew Morton <>
Cc: Ira Weiny <>
Cc: Jan Kara <>
Cc: Jérôme Glisse <>
Cc: Al Viro <>
Cc: Christoph Hellwig <>
Cc: Dan Williams <>
Cc: Dave Chinner <>
Cc: Jason Gunthorpe <>
Cc: Jonathan Corbet <>
Cc: Michal Hocko <>
Cc: Mike Kravetz <>
Cc: Shuah Khan <>
Cc: Vlastimil Babka <>

Signed-off-by: default avatarLinus Torvalds <>
parent be871411
......@@ -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),
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));
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);
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