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SubjectLocal execution of ipi_sync_rq_state() on sync_runqueues_membarrier_state()
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Hello Mathieu,

While trying to find some unrelated by, something in
sync_runqueues_membarrier_state() caught my eye:


static int sync_runqueues_membarrier_state(struct mm_struct *mm)
{
if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
this_cpu_write(runqueues.membarrier_state, membarrier_state);

/*
* For single mm user, we can simply issue a memory barrier
* after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the
* mm and in the current runqueue to guarantee that no memory
* access following registration is reordered before
* registration.
*/
smp_mb();
return 0;
}

[ snip ]

smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);


And ipi_sync_rq_state() does:

this_cpu_write(runqueues.membarrier_state,
atomic_read(&mm->membarrier_state));


So my question: are you aware smp_call_function_many() would not run
ipi_sync_rq_state() on the local CPU? Is that the intention of the code?

Thanks,
Nadav

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