linux-kernel - [PATCH] exit: make setting exit

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Date:   Mon, 29 Jul 2019 18:27:57 +0200
From:   Christian Brauner <christian@...uner.io>
To:     oleg@...hat.com, linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, tj@...nel.org, tglx@...utronix.de,
        prsood@...eaurora.org, avagin@...il.com,
        Christian Brauner <christian@...uner.io>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] exit: make setting exit_state consistent

Since commit [1] we unconditionally set exit_state to EXIT_ZOMBIE before
calling into do_notify_parent(). This was done to eliminate a race when
querying exit_state in do_notify_pidfd().
Back then we decided to do the absolute minimal thing to fix this and
not touch the rest of the exit_notify() function where exit_state is
set.
Since this fix has not caused any issues change the setting of
exit_state to EXIT_DEAD in the autoreap case to account for the fact hat
exit_state is set to EXIT_ZOMBIE unconditionally. This fix was planned
but also explicitly requested in [2] and makes the whole code more
consistent.

/* References */
[1]: b191d6491be6 ("pidfd: fix a poll race when setting exit_state")
[2]: https://lore.kernel.org/lkml/CAHk-=wigcxGFR2szue4wavJtH5cYTTeNES=toUBVGsmX0rzX+g@mail.gmail.com

Signed-off-by: Christian Brauner <christian@...uner.io>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
 kernel/exit.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 4436158a6d30..5b4a5dcce8f8 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -734,9 +734,10 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
 		autoreap = true;
 	}

-	tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE;
-	if (tsk->exit_state == EXIT_DEAD)
+	if (autoreap) {
+		tsk->exit_state = EXIT_DEAD;
 		list_add(&tsk->ptrace_entry, &dead);
+	}

 	/* mt-exec, de_thread() is waiting for group leader */
 	if (unlikely(tsk->signal->notify_count < 0))
-- 
2.22.0