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Date:   Thu, 28 Apr 2022 12:38:07 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     linux-kernel@vger.kernel.org, rjw@rjwysocki.net,
        Oleg Nesterov <oleg@redhat.com>, mingo@kernel.org,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de,
        Will Deacon <will@kernel.org>, tj@kernel.org,
        linux-pm@vger.kernel.org, Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um@lists.infradead.org, Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        inux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with
 siglock held
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References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org>
 <20220426225211.308418-6-ebiederm@xmission.com>
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On Tue, Apr 26, 2022 at 05:52:08PM -0500, Eric W. Biederman wrote:
> Now that siglock keeps tsk->parent and tsk->real_parent constant
> require that do_notify_parent_cldstop is called with tsk->siglock held
> instead of the tasklist_lock.
> 
> As all of the callers of do_notify_parent_cldstop had to drop the
> siglock and take tasklist_lock this simplifies all of it's callers.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  kernel/signal.c | 156 +++++++++++++++++-------------------------------
>  1 file changed, 55 insertions(+), 101 deletions(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 72d96614effc..584d67deb3cb 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2121,11 +2121,13 @@ static void do_notify_parent_cldstop(struct task_struct *tsk,
>  				     bool for_ptracer, int why)
>  {
>  	struct kernel_siginfo info;
> -	unsigned long flags;
>  	struct task_struct *parent;
>  	struct sighand_struct *sighand;
> +	bool lock;
>  	u64 utime, stime;
>  
> +	assert_spin_locked(&tsk->sighand->siglock);

lockdep_assert_held() please...