On Wed, Aug 10, 2016 at 07:33:38AM -0700, Laura Abbott wrote: > Hi, > > There have been several reports[1] of assertions tripping when using > tcpdump on the latest master: > > [ 1013.718212] device wlp2s0 entered promiscuous mode > [ 1013.736003] page:ffffea0004380000 count:2 mapcount:0 mapping: > (null) index:0x0 compound_mapcount: 0 > [ 1013.736013] flags: 0x17ffffc0004000(head) > [ 1013.736017] page dumped because: VM_BUG_ON_PAGE(!PageLocked(page)) > [ 1013.736044] ------------[ cut here ]------------ > [ 1013.736091] kernel BUG at mm/rmap.c:1288! The patch below should do the trick. >From 8026e3a2cecb7cdd3a63ebc266fb359ef7ec965b Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Wed, 10 Aug 2016 18:51:54 +0300 Subject: [PATCH] mm, rmap: fix false positive VM_BUG() in page_add_file_rmap() PageTransCompound() doesn't distinguish THP from from any other type of compound pages. This can lead to false-positive VM_BUG_ON() in page_add_file_rmap() if called on compound page from a driver[1]. I think we can exclude such cases by checking if the page belong to a mapping. The VM_BUG_ON_PAGE() is downgraded to VM_WARN_ON_ONCE(). This path should not cause any harm to non-THP page, but good to know if we step on anything else. [1] http://lkml.kernel.org/r/c711e067-0bff-a6cb-3c37-04dfe77d2db1@xxxxxxxxxx Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: Laura Abbott <labbott@xxxxxxxxxx> --- mm/rmap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index eee844997bd8..f071d6f7a986 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1286,8 +1286,9 @@ void page_add_file_rmap(struct page *page, bool compound) else __inc_node_page_state(page, NR_FILE_PMDMAPPED); } else { - if (PageTransCompound(page)) { - VM_BUG_ON_PAGE(!PageLocked(page), page); + if (PageTransCompound(page) && page_mapping(page)) { + VM_WARN_ON_ONCE(!PageLocked(page)); + SetPageDoubleMap(compound_head(page)); if (PageMlocked(page)) clear_page_mlock(compound_head(page)); -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>