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Date:   Thu, 9 Apr 2020 09:02:53 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Peter Xu <peterx@redhat.com>
Cc:     linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com
Subject: Re: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal
 signal
Message-ID: <20200409070253.GB18386@dhcp22.suse.cz>
References: <20200408014010.80428-1-peterx@redhat.com>
 <20200408014010.80428-2-peterx@redhat.com>
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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