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authorJohn Hubbard <jhubbard@nvidia.com>2020-08-06 23:19:51 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 11:33:23 -0700
commit6dc5ea16c86f753951f53085aa04df49cf17cb50 (patch)
tree46419bf658f6133fec008c00f845e79a4f2e47b7
parent54a75157d97976f35e63e37e31e39bda622cbf39 (diff)
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mm, dump_page: do not crash with bad compound_mapcount()
If a compound page is being split while dump_page() is being run on that page, we can end up calling compound_mapcount() on a page that is no longer compound. This leads to a crash (already seen at least once in the field), due to the VM_BUG_ON_PAGE() assertion inside compound_mapcount(). (The above is from Matthew Wilcox's analysis of Qian Cai's bug report.) A similar problem is possible, via compound_pincount() instead of compound_mapcount(). In order to avoid this kind of crash, make dump_page() slightly more robust, by providing a pair of simpler routines that don't contain assertions: head_mapcount() and head_pincount(). For debug tools, we don't want to go *too* far in this direction, but this is a simple small fix, and the crash has already been seen, so it's a good trade-off. Reported-by: Qian Cai <cai@lca.pw> Suggested-by: Matthew Wilcox <willy@infradead.org> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: William Kucharski <william.kucharski@oracle.com> Link: http://lkml.kernel.org/r/20200804214807.169256-1-jhubbard@nvidia.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/mm.h14
-rw-r--r--mm/debug.c6
2 files changed, 15 insertions, 5 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index dc7b87310c10..303a47a9769d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -779,6 +779,11 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags)
extern void kvfree(const void *addr);
extern void kvfree_sensitive(const void *addr, size_t len);
+static inline int head_mapcount(struct page *head)
+{
+ return atomic_read(compound_mapcount_ptr(head)) + 1;
+}
+
/*
* Mapcount of compound page as a whole, does not include mapped sub-pages.
*
@@ -788,7 +793,7 @@ static inline int compound_mapcount(struct page *page)
{
VM_BUG_ON_PAGE(!PageCompound(page), page);
page = compound_head(page);
- return atomic_read(compound_mapcount_ptr(page)) + 1;
+ return head_mapcount(page);
}
/*
@@ -901,11 +906,16 @@ static inline bool hpage_pincount_available(struct page *page)
return PageCompound(page) && compound_order(page) > 1;
}
+static inline int head_pincount(struct page *head)
+{
+ return atomic_read(compound_pincount_ptr(head));
+}
+
static inline int compound_pincount(struct page *page)
{
VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
page = compound_head(page);
- return atomic_read(compound_pincount_ptr(page));
+ return head_pincount(page);
}
static inline void set_compound_order(struct page *page, unsigned int order)
diff --git a/mm/debug.c b/mm/debug.c
index 8f569db9a514..ca8d1cacdecc 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -102,12 +102,12 @@ void __dump_page(struct page *page, const char *reason)
if (hpage_pincount_available(page)) {
pr_warn("head:%p order:%u compound_mapcount:%d compound_pincount:%d\n",
head, compound_order(head),
- compound_mapcount(head),
- compound_pincount(head));
+ head_mapcount(head),
+ head_pincount(head));
} else {
pr_warn("head:%p order:%u compound_mapcount:%d\n",
head, compound_order(head),
- compound_mapcount(head));
+ head_mapcount(head));
}
}
if (PageKsm(page))