linux-kernel - Re: [PATCH v2 2/2] pidfs: ensure consistent ENOENT/ESRCH reporting

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Message-ID: <20250411135445.GF5322@redhat.com>
Date: Fri, 11 Apr 2025 15:54:45 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
	Lennart Poettering <lennart@...ttering.net>,
	Daan De Meyer <daan.j.demeyer@...il.com>,
	Mike Yuan <me@...dnzj.com>, linux-kernel@...r.kernel.org,
	Peter Ziljstra <peterz@...radead.org>
Subject: Re: [PATCH v2 2/2] pidfs: ensure consistent ENOENT/ESRCH reporting

For both patches:

Reviewed-by: Oleg Nesterov <oleg@...hat.com>

a minor nit below...

On 04/11, Christian Brauner wrote:
>
>  int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
>  {
> -	int err = 0;
> -
> -	if (!(flags & PIDFD_THREAD)) {
> +	scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
> +		/*
> +		 * If this wasn't a thread-group leader struct pid or
> +		 * the task already been reaped report ESRCH to
> +		 * userspace.
> +		 */
> +		if (!pid_has_task(pid, PIDTYPE_PID))
> +			return -ESRCH;

The "If this wasn't a thread-group leader struct pid" part of the
comment looks a bit confusing to me, as if pid_has_task(PIDTYPE_PID)
should return false in this case.

OTOH, perhaps it makes sense to explain scoped_guard(wait_pidfd.lock)?
Something like "see unhash_process -> wake_up_all(), detach_pid(TGID)
isn't possible if pid_has_task(PID) succeeds".

Oleg.