__guarded_by(9)

💅 __guarded_by — a Kernel API Manual moment (that's the 9 section bestie, iykyk)

okay so. bestie. imagine a variable that is SO iconic it refuses to be touched by just anyone. it has a whole security detail. that's this. that's __guarded_by. it's the struct member / globals attribute that declares a variable is only accessible from inside the active context, and honestly? main character energy. 🔥

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✨ NAME ✨

__guarded_by — the struct member and globals attribute that declares a variable is only accessible within the active context.

periodt. that's the whole vibe. 💅

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🌸 SYNOPSIS 🌸

__guarded_by (... );

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🎀 ARGUMENTS 🎀

• ... — the context lock instance pointer(s). that's it. that's the argument. 🫶

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💖 DESCRIPTION 💖

so here's the tea ☕ — __guarded_by declares that a struct member or a global variable is ONLY accessible within the context entered by the given context lock(s). it's literally a velvet rope for your data. ✨

and the rules are very specific, ngl, so pay attention:

• read operations on the data require shared access to at least one of the context locks 👀
• write operations require exclusive access to ALL listed context locks 👑

one lock is enough to read, but you need the whole squad for a write. no cap. that's the deal.

like, here's a lil struct with one lock:

struct some_state {
        spinlock_t lock;
        long counter __guarded_by(lock);
};

and here's one going full "more is more" with two locks:

struct some_state {
        spinlock_t lock1, lock2;
        long counter __guarded_by(lock1, lock2);
};

obsessed. both of them. iconique. 🌈

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🦋 SEE ALSO 🦋

the lore goes deep, bestie — there's an entire friend group:

• Kernel file ./include/linux/compiler-context-analysis.h 📁 (go read it, i'm serious)
• __pt_guarded_by(9)
• context_lock_struct(9)
• disable_context_analysis(9)
• enable_context_analysis(9)
• __no_context_analysis(9)
• context_unsafe(9)
• __context_unsafe(9)
• context_unsafe_alias(9)
• token_context_lock(9)
• token_context_lock_instance(9)
• __must_hold(9)
• __must_not_hold(9)
• __acquires(9)
• __cond_acquires(9)
• __releases(9)
• __cond_releases(9)
• __acquire(9)
• __release(9)
• __must_hold_shared(9)
• __acquires_shared(9)
• __cond_acquires_shared(9)
• __releases_shared(9)
• __acquire_shared(9)
• __release_shared(9)
• __acquire_ret(9)
• __acquire_shared_ret(9)

like. that's twenty-six more manpages. a whole group chat. 💀

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💜 oh and one more thing — standard manpage boilerplate says you can always find this one linked through the kernel file ./include/linux and that this particular glow-up dropped October 2026, and yeah the page is literally called __guarded_by(9) in case you forgot (how?? 😭). stay safe out there and respect the locks. muah. 💋🌸🦋

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