From 2d3a36a47964371101d9a71691c18d59ee611e87 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 3 Jun 2020 16:03:25 -0700 Subject: mm, mempolicy: fix up gup usage in lookup_node ba841078cd05 ("mm/mempolicy: Allow lookup_node() to handle fatal signal") has added a special casing for 0 return value because that was a possible gup return value when interrupted by fatal signal. This has been fixed by ae46d2aa6a7f ("mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal") in the mean time so ba841078cd05 can be reverted. This patch however doesn't go all the way to revert it because the check for 0 is wrong and confusing here. Firstly it is inherently unsafe to access the page when get_user_pages_locked returns 0 (aka no page returned). Fortunatelly this will not happen because get_user_pages_locked will not return 0 when nr_pages > 0 unless FOLL_NOWAIT is specified which is not the case here. Document this potential error code in gup code while we are at it. Signed-off-by: Michal Hocko Signed-off-by: Andrew Morton Cc: Peter Xu Link: http://lkml.kernel.org/r/20200421071026.18394-1-mhocko@kernel.org Signed-off-by: Linus Torvalds --- mm/mempolicy.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'mm/mempolicy.c') diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 48ba9729062ea..1965e26818773 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -927,10 +927,7 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr) int locked = 1; err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked); - if (err == 0) { - /* E.g. GUP interrupted by fatal signal */ - err = -EFAULT; - } else if (err > 0) { + if (err > 0) { err = page_to_nid(p); put_page(p); } -- cgit 1.2.3-korg