linux-kernel - Re: [PATCH] drivers: base: power: Fix GFP

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Date:   Tue, 12 Dec 2017 15:58:00 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     shrikant.maurya@...hveda.org
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Suniel Mahesh <sunil.m@...hveda.org>,
        Karthik Tummala <karthik@...hveda.org>, raghu@...hveda.org
Subject: Re: [PATCH] drivers: base: power: Fix GFP_KERNEL in spinlock context

Hi Shrikant,

On Tue, Dec 12, 2017 at 2:45 PM,  <shrikant.maurya@...hveda.org> wrote:
> From: Shrikant Maurya <shrikant.maurya@...hveda.org>
>
> As reported by Jia-Ju Bai (https://lkml.org/lkml/2017/12/11/872):
> API's are using GFP_KERNEL to allocate memory which may sleep.
>
> To ensure atomicity such allocations must be avoided in critical
> sections under spinlock.
> Fixed by replacing GFP_KERNEL to GFP_ATOMIC.
>
> Reported-by: Jia-Ju Bai <baijiaju1990@...il.com>
> Signed-off-by: Shrikant Maurya <shrikant.maurya@...hveda.org>
> Signed-off-by: Suniel Mahesh <sunil.m@...hveda.org>
> Signed-off-by: Raghu Bharadwaj <raghu@...hveda.org>
> Signed-off-by: Karthik Tummala <karthik@...hveda.org>

Can't the call to device_init_wakeup() in isp116x_start() just be moved
below the spinlock release?

> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -92,11 +92,11 @@ struct wakeup_source *wakeup_source_create(const char *name)
>  {
>         struct wakeup_source *ws;
>
> -       ws = kmalloc(sizeof(*ws), GFP_KERNEL);
> +       ws = kmalloc(sizeof(*ws), GFP_ATOMIC);

With GFP_ATOMIC, allocation failure is much more likely to occur.
So IMHO it's better to fix the isp116x, than to impose this burden on
every user.

>         if (!ws)
>                 return NULL;
>
> -       wakeup_source_prepare(ws, name ? kstrdup_const(name, GFP_KERNEL) : NULL);
> +       wakeup_source_prepare(ws, name ? kstrdup_const(name, GFP_ATOMIC) : NULL);
>         return ws;
>  }
>  EXPORT_SYMBOL_GPL(wakeup_source_create);

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds