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

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Date:   Sat, 16 Dec 2017 13:44:57 +0530
From:   shrikant <shrikant.maurya@...hveda.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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


On Tuesday 12 December 2017 08:28 PM, Geert Uytterhoeven wrote:
> 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?

Can't move it below the spinlock.
Value going to be written into HcRhStatus register depends on it:
isp116x_write_reg32(isp116x, HCRHSTATUS, val);

Instead we can move it before the spinlock.

> 
>> --- 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.

Absolutely. Thanks for pointing it out, it's not the right solution.

> 
>>         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
> 

Thank you Geert.
-- 
Shrikant
techveda.org