percpu-refcount: implement percpu_ref_cancel_init()
Normally, percpu_ref_init() initializes and percpu_ref_kill() initiates destruction which completes asynchronously. The asynchronous destruction can be problematic in init failure path where the caller wants to destroy half-constructed object - distinguishing half-constructed objects from the usual release method can be painful for complex objects. This patch implements percpu_ref_cancel_init() which synchronously destroys the percpu_ref without invoking release. To avoid unintentional misuses, the function requires the ref to have finished percpu_ref_init() but never used and triggers WARN otherwise. v2: Explain the weird name and usage restriction in the function comment. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Kent Overstreet <koverstreet@google.com>
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@ -68,6 +68,7 @@ struct percpu_ref {
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int __must_check percpu_ref_init(struct percpu_ref *ref,
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percpu_ref_func_t *release);
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void percpu_ref_cancel_init(struct percpu_ref *ref);
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void percpu_ref_kill(struct percpu_ref *ref);
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#define PCPU_STATUS_BITS 2
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@ -54,6 +54,37 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
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return 0;
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}
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/**
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* percpu_ref_cancel_init - cancel percpu_ref_init()
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* @ref: percpu_ref to cancel init for
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*
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* Once a percpu_ref is initialized, its destruction is initiated by
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* percpu_ref_kill() and completes asynchronously, which can be painful to
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* do when destroying a half-constructed object in init failure path.
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*
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* This function destroys @ref without invoking @ref->release and the
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* memory area containing it can be freed immediately on return. To
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* prevent accidental misuse, it's required that @ref has finished
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* percpu_ref_init(), whether successful or not, but never used.
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*
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* The weird name and usage restriction are to prevent people from using
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* this function by mistake for normal shutdown instead of
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* percpu_ref_kill().
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*/
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void percpu_ref_cancel_init(struct percpu_ref *ref)
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{
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unsigned __percpu *pcpu_count = ref->pcpu_count;
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int cpu;
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WARN_ON_ONCE(atomic_read(&ref->count) != 1 + PCPU_COUNT_BIAS);
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if (pcpu_count) {
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for_each_possible_cpu(cpu)
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WARN_ON_ONCE(*per_cpu_ptr(pcpu_count, cpu));
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free_percpu(ref->pcpu_count);
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}
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}
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static void percpu_ref_kill_rcu(struct rcu_head *rcu)
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{
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struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
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