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

From: Jia-Ju Bai
Date: Fri Jan 26 2018 - 09:17:37 EST




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