Andrea Righi reported a case where an exiting task can race against ksmd. ksm_scan.mm_slot == the only registered mm CPU 1 (bug program) CPU 2 (ksmd) list_empty() is false lock ksm_scan.mm_slot list_del unlock slot == &ksm_mm_head (but list is now empty_) Close this race by revalidating that the new slot is not simply the list head again. Reported-by: Andrea Righi <andrea@xxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx> --- mm/ksm.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 942dfc7..0373ce4 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1301,6 +1301,9 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); ksm_scan.mm_slot = slot; spin_unlock(&ksm_mmlist_lock); + /* We raced against exit of last slot on the list */ + if (slot == &ksm_mm_head) + return NULL; next_mm: ksm_scan.address = 0; ksm_scan.rmap_list = &slot->rmap_list; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>