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Subject: Re: [PATCH] atm: firestream: Replace GFP_ATOMIC with GFP_KERNEL in
 fs_send
To:     David Miller <davem@davemloft.net>, viro@ZenIV.linux.org.uk
Cc:     3chas3@gmail.com, linux-atm-general@lists.sourceforge.net,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1516953627-30983-1-git-send-email-baijiaju1990@gmail.com>
 <20180126120522.GX13338@ZenIV.linux.org.uk>
 <20180126.110739.419621238821097728.davem@davemloft.net>
From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Message-ID: <e0c42ff6-94f3-580b-f4ae-782aa93a0696@gmail.com>
Date:   Sat, 27 Jan 2018 00:17:53 +0800
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On 2018/1/27 0:07, David Miller wrote:
> From: Al Viro <viro@ZenIV.linux.org.uk>
> Date: Fri, 26 Jan 2018 12:05:22 +0000
>
>> On Fri, Jan 26, 2018 at 04:00:27PM +0800, Jia-Ju Bai wrote:
>>> After checking all possible call chains to fs_send() here,
>>> my tool finds that fs_send() is never called in atomic context.
>>> And this function is assigned to a function pointer "dev->ops->send",
>>> which is only called by vcc_sendmsg() (net/atm/common.c)
>>> through vcc->dev->ops->send(), and vcc_sendmsg() calls schedule(),
>>> it indicates that fs_send() can call functions which may sleep.
>>> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>>>
>>> This is found by a static analysis tool named DCNS written by myself.
>> The trouble is, places like
>> net/atm/raw.c:65:       vcc->send = atm_send_aal0;
>> net/atm/raw.c:74:       vcc->send = vcc->dev->ops->send;
>> net/atm/raw.c:83:       vcc->send = vcc->dev->ops->send;
>> mean extra call chains.  It's *not* just vcc_sendmsg(), and e.g.
>>          ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
>>              ? DROP_PACKET : 1;
>>          bh_unlock_sock(sk_atm(vcc));
>> in pppoatm_send() definitely is called under a spinlock.
>>
>> Looking through the driver (in advanced bitrot, as usual for drivers/atm),
>> I'd say that submit_queue() is fucked in head in the "queue full" case.
>> And judging by the history, had been thus since the original merge...
> Jia-Ju, I'm probably not going to apply any of your GFP_KERNEL
> conversions.
>
> Al's analysis above is similar to how things looked for other patches
> you submited of this nature.
>
> So because of the lack of care and serious auditing you put into these
> conversions, I really have no choice but to drop them from my queue
> because on the whole they are adding bugs rather than improving the
> code.
>
> Thank you.

Okay, I can understand that careless GFP_KERNEL conversions will 
introduce bugs.
Your concern is right.
Sorry for my previous incorrect patches...
I will manually carefully check and audit my patches before I submit them.


Thanks,
Jia-Ju Bai