linux-kernel - Re: [PATCH] x86: avoid calling arch_trigger_all_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <4CDBCCC8.4030104@windriver.com>
Date:	Thu, 11 Nov 2010 19:00:24 +0800
From:	DDD <dongdong.deng@...driver.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	dzickus@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at
 the same time on SMP

Ingo Molnar wrote:
> * DDD <dongdong.deng@...driver.com> wrote:
> 
>> Ingo Molnar wrote:
>>> * Dongdong Deng <dongdong.deng@...driver.com> wrote:
>>>
>>>> +static int backtrace_flag;
>>>> +	if (cmpxchg(&backtrace_flag, 0, 1) != 0)
>>> Sorry to be a PITA, but i asked for test_and_set() because that's
>>> the simplest primitive. cmpxchg() semantics is not nearly as
>>> obvious and people regularly get it wrong :-/
>> As the 'backtrace_flag' could be accessed by multi-cpus on SMP at
>> the same time, I use cmpxchg() for getting a atomic/memory barrier
>> operation for 'backtrace_flag' variable.
>>
>> If we use test_and_set, maybe we need smp_wmb() after test_and_set.
>> (If I wrong, please correct me, thanks. :-) )
> 
> No, test_and_set_bit() is SMP safe and is an implicit barrier as well - so no 
> smp_wmb() or other barriers are needed.

Yep, the spin_lock of test_and_set_bit() could make sure that.

Thank you very much,
I will send out the new patch quickly. :-)

Dongdong

> 
> Thanks,
> 
> 	Ingo
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/