linux-kernel - Re: [PATCH v2] pinctrl: Add lock to ensure the state atomization

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Message-ID: <CACRpkdb6dkw58GwkqYXTDAQtdLazOLyp1CEjnkxDX2v=TDvvMw@mail.gmail.com>
Date: Wed, 20 Dec 2023 12:02:17 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Maria Yu <quic_aiquny@...cinc.com>
Cc: andersson@...nel.org, kernel@...cinc.com, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2] pinctrl: Add lock to ensure the state atomization

Hi Maria,

On Tue, Dec 12, 2023 at 10:06 AM Maria Yu <quic_aiquny@...cinc.com> wrote:

> Currently pinctrl_select_state is an export symbol and don't have
> effective re-entrance protect design. During async probing of devices
> it's possible to end up in pinctrl_select_state() from multiple
> contexts simultaneously, so make it thread safe.
> More over, when the real racy happened, the system frequently have
> printk message like:
>   "not freeing pin xx (xxx) as part of deactivating group xxx - it is
> already used for some other setting".
> Finally the system crashed after the flood log.
> Add per pinctrl lock to ensure the old state and new state transition
> atomization.
> Also move dev error print message outside the region with interrupts
> disabled.
>
> Fixes: 4198a9b57106 ("pinctrl: avoid reload of p state in list iteration")
> Signed-off-by: Maria Yu <quic_aiquny@...cinc.com>

Overall this looks good!

> @@ -1262,9 +1263,12 @@ static void pinctrl_link_add(struct pinctrl_dev *pctldev,
>  static int pinctrl_commit_state(struct pinctrl *p, struct pinctrl_state *state)
>  {
>         struct pinctrl_setting *setting, *setting2;
> -       struct pinctrl_state *old_state = READ_ONCE(p->state);
> +       struct pinctrl_state *old_state;
>         int ret;
> +       unsigned long flags;
>
> +       spin_lock_irqsave(&p->lock, flags);
(...)
> +       spin_unlock_irqrestore(&p->lock, flags);
(...)
> +       spin_unlock_irqrestore(&p->lock, flags);

Is it possible to use a scoped guard for pinctrl_commit_state()?

#include <linux/cleanup.h>
guard(spinlock_irqsave)(&p->lock);

It saves some code (and no need for flags) and avoid possible
bugs when people add new errorpaths to the code.

Yours,
Linus Walleij