poll_state_...ize_rcu_full(9)

📦 version 7.3.1, in nixpkgs unstable

💖 poll_state_...ize_rcu_full(9) 💖

okay bestie, welcome to the Kernel API Manual — this is your RCU grace-period polling vibe check, and lowkey the whole page ate. No cap. 🫶✨

🌸 NAME 🌸

poll_state_synchronize_rcu_full — Has the specified RCU grace period completed?

🦋 SYNOPSIS 🦋

bool poll_state_synchronize_rcu_full (struct rcu_gp_seq *gsp );

🎀 ARGUMENTS 🎀

  • gsp — the value you got from get_state_synchronize_rcu_full or start_poll_synchronize_rcu_full.

💜 DESCRIPTION 💜

If a full RCU grace period has elapsed since the earlier call from which *gsp was obtained, return true, otherwise return false. If false is returned, it is the caller's responsibility to invoke this function later on until it does return true — yes, bestie, that's your main character responsibility, fr fr. Alternatively, the caller can explicitly wait for a grace period, for example, by passing gsp to cond_synchronize_rcu or by directly invoking synchronize_rcu.

Yes, this function does not take counter wrap into account. But counter wrap is harmless — periodt. If the counter wraps, we have waited for more than a billion grace periods (and way more on a 64-bit system!) 😭🔥. Those needing to keep rcu_gp_seq values for very long time periods (many hours even on 32-bit systems) should check them occasionally and either refresh them or set a flag indicating that the grace period has completed. Alternatively, they can use get_completed_synchronize_rcu_full to get a guaranteed-completed grace-period state.

This function provides the same memory-ordering guarantees that would be provided by a synchronize_rcu that was invoked at the call to the function that provided gsp, and that returned at the end of this function. And this guarantee requires that the root rcu_node structure's ->gp_seq field be checked instead of that of the rcu_state structure. The problem is that the just-ending grace-period's callbacks can be invoked between the time that the root rcu_node structure's ->gp_seq field is updated and the time that the rcu_state structure's ->gp_seq field is updated. Therefore, if a single synchronize_rcu is to cause a subsequent poll_state_synchronize_rcu_full to return true, then the root rcu_node structure is the one that needs to be polled. Highkey important, so stay with me 💅.

🔥 SEE ALSO 🔥

Kernel file: ./kernel/rcu/tree.c. And the whole squad, iykyk:

okay that's the whole page, bestie 💅 source/version: ./kernel/rcu, dated October 2026, for poll_state_...ize_rcu_full(9). bye and slay your grace periods 💖🎀

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