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Message-Id: <1522600912-6208-2-git-send-email-andrea.parri@amarulasolutions.com> Date: Sun, 1 Apr 2018 18:41:50 +0200 From: Andrea Parri <andrea.parri@...rulasolutions.com> To: paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, Andrea Parri <andrea.parri@...rulasolutions.com>, Andrea Parri <parri.andrea@...il.com>, Alan Stern <stern@...land.harvard.edu>, Will Deacon <will.deacon@....com>, Boqun Feng <boqun.feng@...il.com>, Nicholas Piggin <npiggin@...il.com>, David Howells <dhowells@...hat.com>, Jade Alglave <j.alglave@....ac.uk>, Luc Maranget <luc.maranget@...ia.fr>, Akira Yokosawa <akiyks@...il.com> Subject: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() There appeared to be a certain, recurrent uncertainty concerning the semantics of spin_is_locked(), likely a consequence of the fact that this semantics remains undocumented or that it has been historically linked to the (likewise unclear) semantics of spin_unlock_wait(). A recent auditing [1] of the callers of the primitive confirmed that none of them are relying on particular ordering guarantees; document this semantics by adding a docbook header to spin_is_locked(). [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 Signed-off-by: Andrea Parri <parri.andrea@...il.com> Cc: Alan Stern <stern@...land.harvard.edu> Cc: Will Deacon <will.deacon@....com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Boqun Feng <boqun.feng@...il.com> Cc: Nicholas Piggin <npiggin@...il.com> Cc: David Howells <dhowells@...hat.com> Cc: Jade Alglave <j.alglave@....ac.uk> Cc: Luc Maranget <luc.maranget@...ia.fr> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Akira Yokosawa <akiyks@...il.com> Cc: Ingo Molnar <mingo@...hat.com> --- include/linux/spinlock.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 4894d322d2584..2639fdc9a916c 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -380,6 +380,17 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ }) +/** + * spin_is_locked() - Check whether a spinlock is locked. + * @lock: Pointer to the spinlock. + * + * This function is NOT required to provide any memory ordering + * guarantees; it could be used for debugging purposes or, when + * additional synchronization is needed, accompanied with other + * constructs (memory barriers) enforcing the synchronization. + * + * Return: 1, if @lock is (found to be) locked; 0, otherwise. + */ static __always_inline int spin_is_locked(spinlock_t *lock) { return raw_spin_is_locked(&lock->rlock); -- 2.7.4
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