path: root/mm
diff options
authorHugh Dickins <hughd@google.com>2016-03-09 14:08:07 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-09 15:43:42 -0800
commit06b241f32c711d7ca868a0351dd97fe91fd8817b (patch)
tree967c5b098468c0682c9ddffe691dd9248f889717 /mm
parent910154d520c97cd0095a889e6b878041c91111a6 (diff)
mm: __delete_from_page_cache show Bad page if mapped
Commit e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() for compound pages") changed the famous BUG_ON(page_mapped(page)) in __delete_from_page_cache() to VM_BUG_ON_PAGE(page_mapped(page)): which gives us more info when CONFIG_DEBUG_VM=y, but nothing at all when not. Although it has not usually been very helpul, being hit long after the error in question, we do need to know if it actually happens on users' systems; but reinstating a crash there is likely to be opposed :) In the non-debug case, pr_alert("BUG: Bad page cache") plus dump_page(), dump_stack(), add_taint() - I don't really believe LOCKDEP_NOW_UNRELIABLE, but that seems to be the standard procedure now. Move that, or the VM_BUG_ON_PAGE(), up before the deletion from tree: so that the unNULLified page->mapping gives a little more information. If the inode is being evicted (rather than truncated), it won't have any vmas left, so it's safe(ish) to assume that the raised mapcount is erroneous, and we can discount it from page_count to avoid leaking the page (I'm less worried by leaking the occasional 4kB, than losing a potential 2MB page with each 4kB page leaked). Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 24 insertions, 1 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 3461d97ecb30..da7a35d83de7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -195,6 +195,30 @@ void __delete_from_page_cache(struct page *page, void *shadow,
cleancache_invalidate_page(mapping, page);
+ VM_BUG_ON_PAGE(page_mapped(page), page);
+ if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
+ int mapcount;
+ pr_alert("BUG: Bad page cache in process %s pfn:%05lx\n",
+ current->comm, page_to_pfn(page));
+ dump_page(page, "still mapped when deleted");
+ dump_stack();
+ mapcount = page_mapcount(page);
+ if (mapping_exiting(mapping) &&
+ page_count(page) >= mapcount + 2) {
+ /*
+ * All vmas have already been torn down, so it's
+ * a good bet that actually the page is unmapped,
+ * and we'd prefer not to leak it: if we're wrong,
+ * some other bad page check should catch it later.
+ */
+ page_mapcount_reset(page);
+ atomic_sub(mapcount, &page->_count);
+ }
+ }
page_cache_tree_delete(mapping, page, shadow);
page->mapping = NULL;
@@ -205,7 +229,6 @@ void __delete_from_page_cache(struct page *page, void *shadow,
__dec_zone_page_state(page, NR_FILE_PAGES);
if (PageSwapBacked(page))
__dec_zone_page_state(page, NR_SHMEM);
- VM_BUG_ON_PAGE(page_mapped(page), page);
* At this point page must be either written or cleaned by truncate.