rcu_sync_enter(9)

✨ rcu_sync_enter(9) ✨

okay so bestie, welcome to the kernel API manual, section 9 — today's main character is rcu_sync_enter, and she's lowkey iconic 💅

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🎀 NAME 🎀

rcu_sync_enter — force readers onto the slowpath. no cap, that's literally the whole job 🦋

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🌸 SYNOPSIS 🌸

void rcu_sync_enter (struct rcu_sync *rsp );

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💖 ARGUMENTS 💖

• rsp — pointer to the rcu_sync structure you're gonna use for synchronization. that's your girl, she holds the state 🫶

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🔥 DESCRIPTION 🔥

So here's the vibe: this function is for updaters — the ones who need readers to actually use the slowpath while an update is going down. the way that works is, once rcu_sync_enter returns, every single subsequent call to rcu_sync_is_idle comes back false, which is basically the kernel telling readers "stay off your fastpaths, we're busy" 😭✨

And then a later call to rcu_sync_exit re-enables those reader fastpaths. balance restored, periodt 👑

Now the important bit, bestie — pay attention because this is the tea ☕: when rcu_sync_enter is called in isolation, it must wait for a grace period. that's the rule, no shortcuts. however 🙈 — closely spaced calls to rcu_sync_enter can optimize away that grace-period wait via a state machine, and that state machine is implemented by rcu_sync_enter, rcu_sync_exit, and rcu_sync_func. teamwork makes the dream work fr fr 💜

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🌈 SEE ALSO 🌈

• Kernel file ./kernel/rcu/sync.c
• rcu_sync_init(9)
• rcu_sync_func(9)
• rcu_sync_exit(9)
• rcu_sync_dtor(9)

go read those next, iykyk 📚💅

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and that's a wrap, bestie! 🎀 this lil page comes to you from ./kernel/rcu, dated October 2026 — slay, mwah 💋🌸