Messages in this thread |  | | Date | Mon, 2 Apr 2018 12:35:40 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() |
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On Mon, Apr 02, 2018 at 10:03:22AM -0400, Alan Stern wrote: > 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@gmail.com> > > Cc: Alan Stern <stern@rowland.harvard.edu> > > Cc: Will Deacon <will.deacon@arm.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Boqun Feng <boqun.feng@gmail.com> > > Cc: Nicholas Piggin <npiggin@gmail.com> > > Cc: David Howells <dhowells@redhat.com> > > Cc: Jade Alglave <j.alglave@ucl.ac.uk> > > Cc: Luc Maranget <luc.maranget@inria.fr> > > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > Cc: Akira Yokosawa <akiyks@gmail.com> > > Cc: Ingo Molnar <mingo@redhat.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.
Unless someone objects or proposes a different course of action, I will make this change in -rcu.
Thanx, Paul
> Alan > > > + */ > > static __always_inline int spin_is_locked(spinlock_t *lock) > > { > > return raw_spin_is_locked(&lock->rlock); > > >
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