Messages in this thread | | | Date | Thu, 11 Nov 2010 11:01:09 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP |
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* DDD <dongdong.deng@windriver.com> wrote:
> Ingo Molnar wrote: > >* Dongdong Deng <dongdong.deng@windriver.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.
Thanks,
Ingo
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