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

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Message-Id: <20180126.111059.743624766367628826.davem@davemloft.net>
Date:   Fri, 26 Jan 2018 11:10:59 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     baijiaju1990@...il.com
Cc:     viro@...IV.linux.org.uk, 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

From: Jia-Ju Bai <baijiaju1990@...il.com>
Date: Fri, 26 Jan 2018 22:17:08 +0800

> 
> 
> 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 :)

No, _you_ have a check.

All of these patches will be dropped, sorry.