From: Shaokun Zhang <zhangshaokun@hisilicon.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
David Miller <davem@davemloft.net>, <netdev@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <jinyuqi@huawei.com>,
<kuznet@ms2.inr.ac.ru>, <yoshfuji@linux-ipv6.org>,
<edumazet@google.com>, <guoyang2@huawei.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve
Date: Sun, 19 Jan 2020 11:46:23 +0800 [thread overview]
Message-ID: <5fd55696-e46c-4269-c106-79782efb0dd8@hisilicon.com> (raw)
In-Reply-To: <20200117123253.GC14879@hirez.programming.kicks-ass.net>
Hi Peter,
On 2020/1/17 20:32, Peter Zijlstra wrote:
> On Fri, Jan 17, 2020 at 02:54:03PM +0800, Shaokun Zhang wrote:
>> So how about this? ;-)
>>
>> delta = prandom_u32_max(now - old);
>>
>> +#ifdef CONFIG_UBSAN
>> /* Do not use atomic_add_return() as it makes UBSAN unhappy */
>> + old = (u32)atomic_read(p_id);
>> do {
>> - old = (u32)atomic_read(p_id);
>> new = old + delta + segs;
>> - } while (atomic_cmpxchg(p_id, old, new) != old);
>> + } while (!atomic_try_cmpxchg(p_id, &old, new));
>> +#else
>> + new = atomic_add_return(segs + delta, p_id);
>> +#endif
>
> That's crazy, just accept that UBSAN is taking bonghits and ignore it.
> Use atomic_add_return() unconditionally.
We have used the atomic_add_return[1], but it makes the UBSAN unhappy followed
by the comment.
It seems that Eric also agreed to do it if some comments are added. I will do
it later.
Thanks,
Shaokun
[1] https://lkml.org/lkml/2019/7/26/217
>
> .
>
next prev parent reply other threads:[~2020-01-19 3:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 3:23 [PATCH] net: optimize cmpxchg in ip_idents_reserve Shaokun Zhang
2020-01-16 12:27 ` David Miller
2020-01-16 14:05 ` Shaokun Zhang
2020-01-16 15:12 ` Eric Dumazet
2020-01-16 15:19 ` Eric Dumazet
2020-01-17 6:54 ` Shaokun Zhang
2020-01-17 12:32 ` Peter Zijlstra
2020-01-17 16:35 ` Eric Dumazet
2020-01-17 18:03 ` Arvind Sankar
2020-01-17 18:16 ` Eric Dumazet
2020-01-17 18:38 ` Arvind Sankar
2020-01-17 18:48 ` Eric Dumazet
2020-01-20 8:18 ` Peter Zijlstra
2020-05-07 9:12 ` Shaokun Zhang
2020-05-07 13:49 ` Eric Dumazet
2020-01-19 3:46 ` Shaokun Zhang [this message]
2020-01-19 4:12 ` Eric Dumazet
2020-01-21 2:40 ` Shaokun Zhang
2020-01-22 8:49 ` Peter Zijlstra
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