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| author | John Hubbard <jhubbard@nvidia.com> | 2020-08-07 08:19:51 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-08-07 20:33:23 +0200 |
| commit | 6dc5ea16c86f753951f53085aa04df49cf17cb50 (patch) | |
| tree | 46419bf658f6133fec008c00f845e79a4f2e47b7 | |
| parent | mm/debug: print hashed address of struct page (diff) | |
| download | linux-6dc5ea16c86f753951f53085aa04df49cf17cb50.tar.xz linux-6dc5ea16c86f753951f53085aa04df49cf17cb50.zip | |
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.h | 14 | ||||
| -rw-r--r-- | mm/debug.c | 6 |
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)) |