On 2021/5/10 13:59, Hugh Dickins wrote: > This reverts commit 3e96b6a2e9ad929a3230a22f4d64a74671a0720b. > General Protection Fault in rmap_walk_ksm() under memory pressure: > remove_rmap_item_from_tree() needs to take page lock, of course. > I'am really sorry about it! And many thanks for this bugfix! It seems rmap_walk_ksm() relies on the page lock to protect against concurrent modifications to that page's node of the stable tree. Could you please add a comment in remove_rmap_item_from_tree() to clarify this in case similar trouble again? Many thanks! > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > --- > > mm/ksm.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > --- 5.13-rc1/mm/ksm.c 2021-05-09 17:03:44.010422188 -0700 > +++ linux/mm/ksm.c 2021-05-09 22:12:39.403008350 -0700 > @@ -776,11 +776,12 @@ static void remove_rmap_item_from_tree(s > struct page *page; > > stable_node = rmap_item->head; > - page = get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK); > + page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); > if (!page) > goto out; > > hlist_del(&rmap_item->hlist); > + unlock_page(page); > put_page(page); > > if (!hlist_empty(&stable_node->hlist)) > . >
