linux-kernel - Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by dev

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Date:   Mon, 23 May 2022 19:27:00 +0300
From:   Kalle Valo <kvalo@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     duoming@....edu.cn, linux-wireless@...r.kernel.org,
        amitkarwar@...il.com, ganapathi017@...il.com,
        sharvari.harisangam@....com, huxinming820@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, rafael@...nel.org,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH v3] mwifiex: fix sleep in atomic context bugs caused by dev_coredumpv

Greg KH <gregkh@...uxfoundation.org> writes:

> On Mon, May 23, 2022 at 02:31:48PM +0300, Kalle Valo wrote:
>> (adding Johannes)
>> 
>> duoming@....edu.cn writes:
>> 
>> >> > --- a/lib/kobject.c
>> >> > +++ b/lib/kobject.c
>> >> > @@ -254,7 +254,7 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
>> >> >  	if (kobj->name && !fmt)
>> >> >  		return 0;
>> >> >  
>> >> > -	s = kvasprintf_const(GFP_KERNEL, fmt, vargs);
>> >> > +	s = kvasprintf_const(GFP_ATOMIC, fmt, vargs);
>> >> >  	if (!s)
>> >> >  		return -ENOMEM;
>> >> >  
>> >> > @@ -267,7 +267,7 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
>> >> >  	if (strchr(s, '/')) {
>> >> >  		char *t;
>> >> >  
>> >> > -		t = kstrdup(s, GFP_KERNEL);
>> >> > +		t = kstrdup(s, GFP_ATOMIC);
>> >> >  		kfree_const(s);
>> >> >  		if (!t)
>> >> >  			return -ENOMEM;
>> >> 
>> >> Please no, you are hurting the whole kernel because of one odd user.
>> >> Please do not make these calls under atomic context.
>> >
>> > Thanks for your time and suggestions. I will remove the gfp_t
>> > parameter of dev_coredumpv in order to show it could not be used in
>> > atomic context.
>> 
>> In a way it would be nice to be able to call dev_coredump from atomic
>> contexts, though I don't know how practical it actually is.
>
> Dumping core information from atomic context feels very very wrong to
> me.
>
> Why not just not do that?

I was wondering why dev_coredumpm() has the gfp parameter in the first
place. But yeah, removing gfp from devcoredump API altogether sounds
like the best thing to do.

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