Re: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal

Michal Hocko
2020-04-09T07:03:01Z

This patch has been merged and it is actually wrong after ae46d2aa6a7f
has been merged. We can either revert or I suggest just handling >0,
like the patch below:

From 03fbe30ec61e65b0927d0d41bccc7dff5f7eafd8 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Thu, 9 Apr 2020 08:26:57 +0200
Subject: [PATCH] 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 0 return
value is impossible. We always get an error or 1 for a single page
request.

Fixes: ba841078cd05 ("mm/mempolicy: Allow lookup_node() to handle fatal signal")
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
mm/mempolicy.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 48ba9729062e..1965e2681877 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);
}
--
2.25.1

--
Michal Hocko
SUSE Labs