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

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Date:   Sat, 16 Dec 2017 13:45:31 +0530
From:   shrikant <shrikant.maurya@...hveda.org>
To:     Pavel Machek <pavel@....cz>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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 Friday 15 December 2017 02:15 PM, Pavel Machek wrote:
> On Tue 2017-12-12 15:58:00, 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?
>>
>>> --- 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;
> 
> NAK. This will silently replace name with NULL if memory is low.

Yes, replacing GFP_KERNEL with GFP_ATOMIC in both places will cause more 
issues than it fixes.

> 
> 									Pavel
> 

Thank you Pavel.

-- 
Shrikant
techveda.org