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    SubjectRe: [PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv
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    On 2018/1/28 1:48, Ed Cashin wrote:
    > If the tool cannot tell whether the protected state is manipulated by *another* piece of code called in atomic context, then it's insufficient.
    >
    >> On Jan 26, 2018, at 4:37 AM, Jia-Ju Bai <baijiaju1990@gmail.com> wrote:
    >>
    >> After checking all possible call chains to aoenet_rcv(),
    >> my tool finds that aoenet_rcv() is never called in atomic context,
    >> namely never in an interrupt handler or holding a spinlock.
    >> 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.
    >>
    >> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
    >> ---
    >> drivers/block/aoe/aoenet.c | 2 +-
    >> 1 file changed, 1 insertion(+), 1 deletion(-)
    >>
    >> diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
    >> index 63773a9..d5fff7a 100644
    >> --- a/drivers/block/aoe/aoenet.c
    >> +++ b/drivers/block/aoe/aoenet.c
    >> @@ -138,7 +138,7 @@ static int __init aoe_iflist_setup(char *str)
    >> if (dev_net(ifp) != &init_net)
    >> goto exit;
    >>
    >> - skb = skb_share_check(skb, GFP_ATOMIC);
    >> + skb = skb_share_check(skb, GFP_KERNEL);
    >> if (skb == NULL)
    >> return 0;
    >> if (!is_aoe_netif(ifp))
    >> --
    >> 1.7.9.5
    >>
    >>

    Sorry, I find my report is false positive after I manually check the code.
    aoenet_rcv() is used as function pointer via "->func", and it is called
    in dev_queue_xmit_nit() in net/core/dev.c.
    dev_queue_xmit_nit() calls a rcu_read_lock() before it calls
    pt_prev->func().
    Thus it is right to use GFP_ATOMIC in aoenet_rcv().
    Sorry again for my incorrect report...

    Thanks,
    Jia-Ju Bai

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