netdev - Re: [PATCH] core: fix the use of this_cpu

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Message-ID: <CAJFZqHzkGcFT_gcqgu=ktuig7UEoR4FVTUZF6G46=6n6FkYZ2A@mail.gmail.com>
Date:	Fri, 29 Mar 2013 09:24:37 +0800
From:	RongQing Li <roy.qing.li@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Shan Wei <davidshan@...cent.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] core: fix the use of this_cpu_ptr

2013/3/28 Christoph Lameter <cl@...ux.com>:
> On Thu, 28 Mar 2013, Eric Dumazet wrote:
>
>> > flush_tasklet is not percpu var, and percpu is percpu var, and
>> >     this_cpu_ptr(&info->cache->percpu->flush_tasklet)
>> > is not equal to
>> >     &this_cpu_ptr(info->cache->percpu)->flush_tasklet
>
> &this_cpu_ptr is always an error since you are taking the addresss of an
> address.
>

&this_cpu_ptr()->flush_tasklet,   "->" has high priority than "&"
so the result is same as
 &(this_cpu_ptr()->flush_tasklet)
it should not a issue.

flush_tasklet is not a percpu var, it is a member of percpu var.

-Roy

> this_cpu_ptr(&structure) is the right way to get the address of the cpu
> instance for this cpu for a per cpu structure.
>
>> Christoph, could this kind of error be detected by the compiler or
>> sparse ?
>
> The per cpu variables are marked with __percpu. This should be detected by
> sparse.
>
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