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From:   "Joel Fernandes (Google)" <joel@joelfernandes.org>
To:     linux-kernel@vger.kernel.org
Cc:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Christian Brauner <christian@brauner.io>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>
Subject: [PATCH] pidfd: Add warning if exit_state is 0 during notification
Date:   Wed, 24 Jul 2019 12:48:16 -0400
Message-Id: <20190724164816.201099-1-joel@joelfernandes.org>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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Previously a condition got missed where the pidfd waiters are awakened
before the exit_state gets set. This can result in a missed notification
[1] and the polling thread waiting forever.

It is fixed now, however it would be nice to avoid this kind of issue
going unnoticed in the future. So just add a warning to catch it in the
future.

[1] https://lore.kernel.org/lkml/20190717172100.261204-1-joel@joelfernandes.org/

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/signal.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/signal.c b/kernel/signal.c
index 91b789dd6e72..349f5a67f100 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1885,6 +1885,7 @@ static void do_notify_pidfd(struct task_struct *task)
 {
 	struct pid *pid;
 
+	WARN_ON(task->exit_state == 0);
 	pid = task_pid(task);
 	wake_up_all(&pid->wait_pidfd);
 }
-- 
2.22.0.657.g960e92d24f-goog