mirror of https://lore.kernel.org/lkml/
 help / color / mirror / Atom feed
From: Tejun Heo <tj@kernel.org>
To: Andrea Righi <arighi@nvidia.com>
Cc: David Vernet <void@manifault.com>,
	Changwoo Min <changwoo@igalia.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] sched_ext/idle: Make scx_bpf_select_cpu_and() usable from any context
Date: Mon, 12 May 2025 07:19:53 -1000	[thread overview]
Message-ID: <aCItuWh-BLp3jC6h@slm.duckdns.org> (raw)
In-Reply-To: <20250512151743.42988-3-arighi@nvidia.com>

Hello,

On Mon, May 12, 2025 at 05:14:56PM +0200, Andrea Righi wrote:
>  #ifdef CONFIG_SMP
> +	/*
> +	 * If called from an unlocked context, try to acquire
> +	 * cpus_read_lock() to avoid races with CPU hotplug.
> +	 */
> +	if (scx_kf_allowed_if_unlocked())
> +		if (!cpus_read_trylock())
> +			return -EBUSY;

Is this meaningful? The idle CPU selection is already racy against CPU
hotplugs and we depend on the scheduler core to fix it up afterwards. Even
if scx_bpf_select_cpu_and() is not racy, it will drop the cpus lock before
returning and becomes racy again right there. ie. This doesn't add any
meaningful protection.

Thanks.

-- 
tejun

  parent reply	other threads:[~2025-05-12 17:19 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-05-12 15:14 [PATCH sched_ext/for-6.16 0/2] sched_ext: Extend usability of scx_bpf_select_cpu_and() Andrea Righi
2025-05-12 15:14 ` [PATCH 1/2] sched_ext: Make scx_kf_allowed_if_unlocked() available outside ext.c Andrea Righi
2025-05-12 15:14 ` [PATCH 2/2] sched_ext/idle: Make scx_bpf_select_cpu_and() usable from any context Andrea Righi
2025-05-12 16:58   ` David Vernet
2025-05-12 18:29     ` Andrea Righi
2025-05-12 19:07       ` Andrea Righi
2025-05-12 20:00         ` Tejun Heo
2025-05-13  5:23           ` Andrea Righi
2025-05-12 17:19   ` Tejun Heo [this message]
2025-05-12 18:35     ` Andrea Righi
2025-05-13  0:46 ` [PATCH sched_ext/for-6.16 0/2] sched_ext: Extend usability of scx_bpf_select_cpu_and() Changwoo Min
2025-05-13  5:48   ` Andrea Righi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=aCItuWh-BLp3jC6h@slm.duckdns.org \
    --to=tj@kernel.org \
    --cc=arighi@nvidia.com \
    --cc=changwoo@igalia.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=void@manifault.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®