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Re: [Xen-devel] [PATCH 2/2] xen/rcu: don't use stop_machine_run() for rcu_barrier()

On 17.02.20 12:49, Julien Grall wrote:
Hi Juergen,

On 17/02/2020 07:20, Juergen Gross wrote:
+void rcu_barrier(void)
-    atomic_t cpu_count = ATOMIC_INIT(0);
-    return stop_machine_run(rcu_barrier_action, &cpu_count, NR_CPUS);
+    if ( !atomic_cmpxchg(&cpu_count, 0, num_online_cpus()) )

What does prevent the cpu_online_map to change under your feet? Shouldn't you grab the lock via get_cpu_maps()?

Oh, indeed.

This in turn will require a modification of the logic to detect parallel
calls on multiple cpus.


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