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authorVlastimil Babka <vbabka@suse.cz>2019-07-11 20:55:09 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-07-12 11:05:43 -0700
commit4462b32c9285b521ef378907aa66a5ca485aae41 (patch)
tree5ee9a6626c5882da5f9dec5106f2fe5fd02097d8 /mm/Kconfig.debug
parent96a2b03f281d3a3b29c27028164f43090d6495b9 (diff)
downloadlwn-4462b32c9285b521ef378907aa66a5ca485aae41.tar.gz
lwn-4462b32c9285b521ef378907aa66a5ca485aae41.zip
mm, page_alloc: more extensive free page checking with debug_pagealloc
The page allocator checks struct pages for expected state (mapcount, flags etc) as pages are being allocated (check_new_page()) and freed (free_pages_check()) to provide some defense against errors in page allocator users. Prior commits 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP") and 4db7548ccbd9 ("mm, page_alloc: defer debugging checks of freed pages until a PCP drain") this has happened for order-0 pages as they were allocated from or freed to the per-cpu caches (pcplists). Since those are fast paths, the checks are now performed only when pages are moved between pcplists and global free lists. This however lowers the chances of catching errors soon enough. In order to increase the chances of the checks to catch errors, the kernel has to be rebuilt with CONFIG_DEBUG_VM, which also enables multiple other internal debug checks (VM_BUG_ON() etc), which is suboptimal when the goal is to catch errors in mm users, not in mm code itself. To catch some wrong users of the page allocator we have CONFIG_DEBUG_PAGEALLOC, which is designed to have virtually no overhead unless enabled at boot time. Memory corruptions when writing to freed pages have often the same underlying errors (use-after-free, double free) as corrupting the corresponding struct pages, so this existing debugging functionality is a good fit to extend by also perform struct page checks at least as often as if CONFIG_DEBUG_VM was enabled. Specifically, after this patch, when debug_pagealloc is enabled on boot, and CONFIG_DEBUG_VM disabled, pages are checked when allocated from or freed to the pcplists *in addition* to being moved between pcplists and free lists. When both debug_pagealloc and CONFIG_DEBUG_VM are enabled, pages are checked when being moved between pcplists and free lists *in addition* to when allocated from or freed to the pcplists. When debug_pagealloc is not enabled on boot, the overhead in fast paths should be virtually none thanks to the use of static key. Link: http://lkml.kernel.org/r/20190603143451.27353-3-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/Kconfig.debug')
-rw-r--r--mm/Kconfig.debug13
1 files changed, 9 insertions, 4 deletions
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index fa6d79281368..a35ab6c55192 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -19,12 +19,17 @@ config DEBUG_PAGEALLOC
Depending on runtime enablement, this results in a small or large
slowdown, but helps to find certain types of memory corruption.
+ Also, the state of page tracking structures is checked more often as
+ pages are being allocated and freed, as unexpected state changes
+ often happen for same reasons as memory corruption (e.g. double free,
+ use-after-free).
+
For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
fill the pages with poison patterns after free_pages() and verify
- the patterns before alloc_pages(). Additionally,
- this option cannot be enabled in combination with hibernation as
- that would result in incorrect warnings of memory corruption after
- a resume because free pages are not saved to the suspend image.
+ the patterns before alloc_pages(). Additionally, this option cannot
+ be enabled in combination with hibernation as that would result in
+ incorrect warnings of memory corruption after a resume because free
+ pages are not saved to the suspend image.
By default this option will have a small overhead, e.g. by not
allowing the kernel mapping to be backed by large pages on some