Date: Mon, 11 Oct 2010 14:45:03 -0400 From: Jung-uk Kim <jkim@FreeBSD.org> To: freebsd-hackers@freebsd.org Cc: Matthew Fleming <mdf@freebsd.org>, Andriy Gapon <avg@freebsd.org> Subject: Re: generic_stop_cpus: prevent parallel execution Message-ID: <201010111445.14920.jkim@FreeBSD.org> In-Reply-To: <201010111211.37993.jhb@freebsd.org> References: <4CAE092A.60905@freebsd.org> <201010111211.37993.jhb@freebsd.org>
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On Monday 11 October 2010 12:11 pm, John Baldwin wrote: > On Thursday, October 07, 2010 1:53:46 pm Andriy Gapon wrote: > > Here is patch that applies the technique from panic() to > > generic_stop_cpus() to prevent its parallel execution on multiple > > CPUs: > > http://people.freebsd.org/~avg/generic_stop_cpus.diff > > > > In theory this could lead to two CPUs stopping each other and > > everyone else, and thus a total system halt. > > > > Also, in theory, we should have some smarter locking here, > > because two (or more CPUs) could be stopping unrelated sets of > > CPUs. But in practice, it seems, this function is only used to > > stop "all other" CPUs. Unless I overlooked other usages, that > > is. > > > > Additionally, I took this opportunity to make amd64-specific > > suspend_cpus() function use generic_stop_cpus() instead of > > rolling out essentially duplicate code. I couldn't see any > > reason no to consolidate, but perhaps I missed something. When I wrote the code, generic_stop_cpus() didn't exist. Now it makes sense, though. > > Big thanks to Matthew and his employer for the idea and example. > > One note. Use 'cpu_spinwait()' in the inner loop waiting for > 'stopping_cpu' to change. +1. Jung-uk Kim
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