netdev - Re: [PATCH] atm: firestream: Replace GFP_ATOMIC with GFP_KERNEL in fs

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Message-ID: <35cb1c70-824b-e0a3-1bed-d147d0f5dec2@gmail.com>
Date:   Fri, 26 Jan 2018 22:17:08 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     3chas3@...il.com, linux-atm-general@...ts.sourceforge.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] atm: firestream: Replace GFP_ATOMIC with GFP_KERNEL in
 fs_send



On 2018/1/26 21:56, Jia-Ju Bai wrote:
>
>
> On 2018/1/26 20:05, Al Viro wrote:
>> 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...
>
> Thanks for reply :)
>
> I am sorry for this false positive.
> I think other ATM related patches that I submitted are also false 
> positives, sorry.
> My tool did not handle this situation of passing function pointer, and 
> I will improve the tool...
>
>
> Thanks,
> Jia-Ju Bai

I check the code again, and confirm only my patches about "send" are 
false positives.
I think other my patches that are about "open" does not has this problem:
https://marc.info/?l=linux-kernel&m=151693791432626&w=2
https://marc.info/?l=linux-kernel&m=151695475503314&w=2
https://marc.info/?l=linux-kernel&m=151693150131512&w=2

I hope you can have a check :)


Thanks,
Jia-Ju Bai