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Date: Wed, 18 May 2016 19:06:47 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Chris Metcalf <cmetcalf@...lanox.com> Cc: Gilad Ben Yossef <giladb@...hip.com>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>, Frederic Weisbecker <fweisbec@...il.com>, Thomas Gleixner <tglx@...utronix.de>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Christoph Lameter <cl@...ux.com>, Viresh Kumar <viresh.kumar@...aro.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Andy Lutomirski <luto@...capital.net>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v12 07/13] task_isolation: add debug boot flag On Wed, May 18, 2016 at 12:35:19PM -0400, Chris Metcalf wrote: > On 5/18/2016 9:56 AM, Peter Zijlstra wrote: > >On Tue, Apr 05, 2016 at 01:38:36PM -0400, Chris Metcalf wrote: > >>+#ifdef CONFIG_TASK_ISOLATION > >>+void task_isolation_debug(int cpu) > >>+{ > >>+ struct task_struct *p; > >>+ > >>+ if (!task_isolation_possible(cpu)) > >>+ return; > >>+ > >>+ rcu_read_lock(); > >>+ p = cpu_curr(cpu); > >>+ get_task_struct(p); > >>+ rcu_read_unlock(); > >>+ task_isolation_debug_task(cpu, p); > >>+ put_task_struct(p); > > > >This is still broken... > > I don't know how or why, though. :-) Can you give me a better idiom? > This looks to my eye just like how it's done for something like > sched_setaffinity() by one task on another task, and I would have > assumed the risks there of the other task evaporating part way > through would be the same as the risks here. Because rcu_read_lock() does not stop the task pointed to by cpu_curr(cpu) from disappearing on you entirely. See also the discussion around: lkml.kernel.org/r/20160518170218.GY3192@...ns.programming.kicks-ass.net
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