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rethook: honor CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING in rethook_try_get()
Take into account CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING when validating that RCU is watching when trying to setup rethooko on a function entry. One notable exception when we force rcu_is_watching() check is CONFIG_KPROBE_EVENTS_ON_NOTRACE=y case, in which case kretprobes will use old-style int3-based workflow instead of relying on ftrace, making RCU watching check important to validate. This further (in addition to improvements in the previous patch) improves BPF multi-kretprobe (which rely on rethook) runtime throughput by 2.3%, according to BPF benchmarks ([0]). [0] https://lore.kernel.org/bpf/CAEf4BzauQ2WKMjZdc9s0rBWa01BYbgwHN6aNDXQSHYia47pQ-w@mail.gmail.com/ Link: https://lore.kernel.org/all/20240418190909.704286-2-andrii@kernel.org/ Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Paul E. McKenney <paulmck@kernel.org> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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@ -166,6 +166,7 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
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if (unlikely(!handler))
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return NULL;
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#if defined(CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING) || defined(CONFIG_KPROBE_EVENTS_ON_NOTRACE)
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/*
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* This expects the caller will set up a rethook on a function entry.
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* When the function returns, the rethook will eventually be reclaimed
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@ -174,6 +175,7 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
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*/
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if (unlikely(!rcu_is_watching()))
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return NULL;
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#endif
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return (struct rethook_node *)objpool_pop(&rh->pool);
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}
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