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The smp_rendezvous_cpus() function should ensure that all accesses
done by the functions called on other CPUs, are visible to the caller. Pair otherwise useless acquire on smp_rv_waiters[3] with a release add to ensure synchronized with relation, which guarantees visibility. Reviewed by: alc Sponsored by: The FreeBSD Foundation MFC after: 3 weeks
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=285771
@ -455,8 +455,13 @@ smp_rendezvous_action(void)
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* This means that no member of smp_rv_* pseudo-structure will be
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* accessed by this target CPU after this point; in particular,
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* memory pointed by smp_rv_func_arg.
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*
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* The release semantic ensures that all accesses performed by
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* the current CPU are visible when smp_rendezvous_cpus()
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* returns, by synchronizing with the
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* atomic_load_acq_int(&smp_rv_waiters[3]).
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*/
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atomic_add_int(&smp_rv_waiters[3], 1);
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atomic_add_rel_int(&smp_rv_waiters[3], 1);
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td->td_critnest--;
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KASSERT(owepreempt == td->td_owepreempt,
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@ -522,6 +527,11 @@ smp_rendezvous_cpus(cpuset_t map,
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* CPUs to finish the rendezvous, so that smp_rv_*
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* pseudo-structure and the arg are guaranteed to not
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* be in use.
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*
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* Load acquire synchronizes with the release add in
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* smp_rendezvous_action(), which ensures that our caller sees
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* all memory actions done by the called functions on other
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* CPUs.
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*/
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while (atomic_load_acq_int(&smp_rv_waiters[3]) < ncpus)
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cpu_spinwait();
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