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Message-ID: <Pine.LNX.4.44L0.1804021001130.1415-100000@iolanthe.rowland.org> Date: Mon, 2 Apr 2018 10:03:22 -0400 (EDT) From: Alan Stern <stern@...land.harvard.edu> To: Andrea Parri <andrea.parri@...rulasolutions.com> cc: paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, <linux-kernel@...r.kernel.org>, Andrea Parri <parri.andrea@...il.com>, 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: Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() On Sun, 1 Apr 2018, Andrea Parri wrote: > 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. This is a good addition. But please remove the parenthetical phrase. Or if you prefer to keep it, at least remove the parentheses. Alan > + */ > static __always_inline int spin_is_locked(spinlock_t *lock) > { > return raw_spin_is_locked(&lock->rlock); >
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