Messages in this thread | | | Date | Thu, 11 Nov 2010 17:51:33 +0800 | From | DDD <> | Subject | Re: [PATCH] x86: avoid calling arch_trigger_all_cpu_backtrace() at the same time on SMP |
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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. :-) )
Should we still need to use test_and_set? If need, I will use test_and_set at my next patch.
> > Also, variables that cmpxchg or test_and_set operates on need to be long, not int.
Got it, I will change it to 'unsigned long' type.
Thanks for your teaching.
Dongdong
> > Ingo >
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