linux-kernel - [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal

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Date:   Wed,  8 Apr 2020 11:59:24 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>, peterx@...hat.com,
        Hillf Danton <hdanton@...a.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        syzbot+3be1a33f04dc782e9fd5@...kaller.appspotmail.com,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal

From: Hillf Danton <hdanton@...a.com>

__get_user_pages_locked() will return 0 instead of -EINTR after commit
4426e945df588 which added extra code to allow gup detect fatal signal
faster.  Restore that behavior.

Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
Reported-by: syzbot+3be1a33f04dc782e9fd5@...kaller.appspotmail.com
Signed-off-by: Hillf Danton <hdanton@...a.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---

PS. Patch verified with syzbot.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 mm/gup.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index afce0bc47e70..6076df8e04a4 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1326,8 +1326,11 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		 * start trying again otherwise it can loop forever.
 		 */
 
-		if (fatal_signal_pending(current))
+		if (fatal_signal_pending(current)) {
+			if (!pages_done)
+				pages_done = -EINTR;
 			break;
+		}
 
 		ret = down_read_killable(&mm->mmap_sem);
 		if (ret) {
-- 
2.24.1