Re: [PATCH] atm: firestream: Replace GFP_ATOMIC with GFP_KERNEL in fs_send

[Jia-Ju Bai]

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