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Date: Thu, 28 Feb 2019 18:35:31 +0000
From: Vlad Buslov <vladbu@...lanox.com>
To: Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>
CC: Linux Kernel Network Developers <netdev@...r.kernel.org>,
Jamal Hadi Salim <jhs@...atatu.com>,
David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 01/12] net: sched: flower: don't check for rtnl
on head dereference
On Thu 28 Feb 2019 at 00:49, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Tue, Feb 26, 2019 at 6:57 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>>
>>
>> On Mon 25 Feb 2019 at 22:39, Cong Wang <xiyou.wangcong@...il.com> wrote:
>> > On Mon, Feb 25, 2019 at 8:11 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>> >>
>> >>
>> >> On Fri 22 Feb 2019 at 19:32, Cong Wang <xiyou.wangcong@...il.com> wrote:
>> >> >
>> >> > So if it is no longer RCU any more, why do you still use
>> >> > rcu_dereference_protected()? That is, why not just deref it as a raw
>> >> > pointer?
>> >
>> >
>> > Any answer for this question?
>>
>> I decided that since there is neither possibility of concurrent pointer
>> assignment nor deallocation of object that it points to, most performant
>> solution would be using rcu_dereference_protected() which is the only
>> RCU dereference helper that doesn't use READ_ONCE. I now understand that
>> this is confusing (and most likely doesn't provide any noticeable
>> performance improvement anyway!) and will change this patch to use
>> rcu_dereference_raw() as you suggest.
>
> Yeah, please make sure sparse is happy with that. :)
I checked my flower change with sparse. It produced a lot of warnings,
some of which are several years old. None in the code I changed though:
CHECK net/sched/cls_flower.c
net/sched/cls_flower.c:200:20: warning: cast from restricted __be16
net/sched/cls_flower.c:200:20: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:200:20: expected unsigned short [usertype] val
net/sched/cls_flower.c:200:20: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:200:20: warning: cast from restricted __be16
net/sched/cls_flower.c:200:20: warning: cast from restricted __be16
net/sched/cls_flower.c:201:20: warning: cast from restricted __be16
net/sched/cls_flower.c:201:20: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:201:20: expected unsigned short [usertype] val
net/sched/cls_flower.c:201:20: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:201:20: warning: cast from restricted __be16
net/sched/cls_flower.c:201:20: warning: cast from restricted __be16
net/sched/cls_flower.c:202:19: warning: cast from restricted __be16
net/sched/cls_flower.c:202:19: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:202:19: expected unsigned short [usertype] val
net/sched/cls_flower.c:202:19: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:202:19: warning: cast from restricted __be16
net/sched/cls_flower.c:202:19: warning: cast from restricted __be16
net/sched/cls_flower.c:203:19: warning: cast from restricted __be16
net/sched/cls_flower.c:203:19: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:203:19: expected unsigned short [usertype] val
net/sched/cls_flower.c:203:19: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:203:19: warning: cast from restricted __be16
net/sched/cls_flower.c:203:19: warning: cast from restricted __be16
net/sched/cls_flower.c:206:21: warning: cast from restricted __be16
net/sched/cls_flower.c:206:21: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:206:21: expected unsigned short [usertype] val
net/sched/cls_flower.c:206:21: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:206:21: warning: cast from restricted __be16
net/sched/cls_flower.c:206:21: warning: cast from restricted __be16
net/sched/cls_flower.c:206:21: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:206:42: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:207:21: warning: cast from restricted __be16
net/sched/cls_flower.c:207:21: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:207:21: expected unsigned short [usertype] val
net/sched/cls_flower.c:207:21: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:207:21: warning: cast from restricted __be16
net/sched/cls_flower.c:207:21: warning: cast from restricted __be16
net/sched/cls_flower.c:207:21: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:207:42: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:223:20: warning: cast from restricted __be16
net/sched/cls_flower.c:223:20: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:223:20: expected unsigned short [usertype] val
net/sched/cls_flower.c:223:20: got restricted __be16 [usertype] src
net/sched/cls_flower.c:223:20: warning: cast from restricted __be16
net/sched/cls_flower.c:223:20: warning: cast from restricted __be16
net/sched/cls_flower.c:224:20: warning: cast from restricted __be16
net/sched/cls_flower.c:224:20: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:224:20: expected unsigned short [usertype] val
net/sched/cls_flower.c:224:20: got restricted __be16 [usertype] src
net/sched/cls_flower.c:224:20: warning: cast from restricted __be16
net/sched/cls_flower.c:224:20: warning: cast from restricted __be16
net/sched/cls_flower.c:225:19: warning: cast from restricted __be16
net/sched/cls_flower.c:225:19: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:225:19: expected unsigned short [usertype] val
net/sched/cls_flower.c:225:19: got restricted __be16 [usertype] src
net/sched/cls_flower.c:225:19: warning: cast from restricted __be16
net/sched/cls_flower.c:225:19: warning: cast from restricted __be16
net/sched/cls_flower.c:226:19: warning: cast from restricted __be16
net/sched/cls_flower.c:226:19: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:226:19: expected unsigned short [usertype] val
net/sched/cls_flower.c:226:19: got restricted __be16 [usertype] src
net/sched/cls_flower.c:226:19: warning: cast from restricted __be16
net/sched/cls_flower.c:226:19: warning: cast from restricted __be16
net/sched/cls_flower.c:229:21: warning: cast from restricted __be16
net/sched/cls_flower.c:229:21: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:229:21: expected unsigned short [usertype] val
net/sched/cls_flower.c:229:21: got restricted __be16 [usertype] src
net/sched/cls_flower.c:229:21: warning: cast from restricted __be16
net/sched/cls_flower.c:229:21: warning: cast from restricted __be16
net/sched/cls_flower.c:229:21: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:229:42: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:230:21: warning: cast from restricted __be16
net/sched/cls_flower.c:230:21: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:230:21: expected unsigned short [usertype] val
net/sched/cls_flower.c:230:21: got restricted __be16 [usertype] src
net/sched/cls_flower.c:230:21: warning: cast from restricted __be16
net/sched/cls_flower.c:230:21: warning: cast from restricted __be16
net/sched/cls_flower.c:230:21: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:230:42: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:744:14: warning: cast from restricted __be16
net/sched/cls_flower.c:744:14: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:744:14: expected unsigned short [usertype] val
net/sched/cls_flower.c:744:14: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:744:14: warning: cast from restricted __be16
net/sched/cls_flower.c:744:14: warning: cast from restricted __be16
net/sched/cls_flower.c:744:40: warning: cast from restricted __be16
net/sched/cls_flower.c:744:40: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:744:40: expected unsigned short [usertype] val
net/sched/cls_flower.c:744:40: got restricted __be16 [usertype] dst
net/sched/cls_flower.c:744:40: warning: cast from restricted __be16
net/sched/cls_flower.c:744:40: warning: cast from restricted __be16
net/sched/cls_flower.c:744:14: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:744:40: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:746:15: warning: cast from restricted __be16
net/sched/cls_flower.c:746:15: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:746:15: expected unsigned short [usertype] val
net/sched/cls_flower.c:746:15: got restricted __be16 [usertype] src
net/sched/cls_flower.c:746:15: warning: cast from restricted __be16
net/sched/cls_flower.c:746:15: warning: cast from restricted __be16
net/sched/cls_flower.c:746:41: warning: cast from restricted __be16
net/sched/cls_flower.c:746:41: warning: incorrect type in argument 1 (different base types)
net/sched/cls_flower.c:746:41: expected unsigned short [usertype] val
net/sched/cls_flower.c:746:41: got restricted __be16 [usertype] src
net/sched/cls_flower.c:746:41: warning: cast from restricted __be16
net/sched/cls_flower.c:746:41: warning: cast from restricted __be16
net/sched/cls_flower.c:746:15: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:746:41: warning: restricted __be16 degrades to integer
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:830:15: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
net/sched/cls_flower.c:831:16: warning: cast to restricted __be32
Cong, Jiri, do you want me to send patch that fixes all of these first?
Regards,
Vlad
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