Re: [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()

Daniel Walker wrote:

+#else
+	raw_local_irq_disable();
+	oldusage = atomic_read(&t->usage);
+	if (oldusage == 0) {
+		raw_local_irq_enable();
+		return 0;
+	}

Isn't this still racy if another cpu drops the last reference
to task struct here? Or can't that happen?

When you said "disable preempt", I had some silly idea that this
function was only used in PREEMPT_RT mode, and that you would
simply disallow architectures without cmpxchg from configuring
PREEMPT_RT.

+	atomic_inc(&t->usage);
+	raw_local_irq_enable();
+#endif

--
SUSE Labs, Novell Inc.

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---

• References:
  • [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()
    • From: Daniel Walker <[email protected]>
  • Re: [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()
    • From: Nick Piggin <[email protected]>
  • Re: [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()
    • From: Daniel Walker <[email protected]>
  • Re: [PATCH] RT: Checks for cmpxchg in get_task_struct_rcu()
    • From: Daniel Walker <[email protected]>

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