Messages in this thread | | | Date | Sun, 8 Apr 2018 15:00:21 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v4 1/3] locking: Document the semantics of spin_is_locked() |
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On Sun, Apr 08, 2018 at 02:32:53PM -0700, Randy Dunlap wrote: > On 04/08/2018 02:14 PM, Paul E. McKenney wrote: > > On Fri, Apr 06, 2018 at 11:58:25PM +0200, Andrea Parri wrote: > >> On Fri, Apr 06, 2018 at 02:08:16PM -0700, Randy Dunlap wrote: > >>> On 04/06/2018 02:07 PM, Paul E. McKenney wrote: > >>>> On Fri, Apr 06, 2018 at 02:01:41PM -0700, Randy Dunlap wrote: > >>>>> On 04/06/2018 12:47 PM, 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(). Also, > >>>>>> describe behaviors specific to certain CONFIG_SMP=n builds. > >>>>>> > >>>>>> [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 > >>>>>> https://marc.info/?l=linux-kernel&m=152042843808540&w=2 > >>>>>> https://marc.info/?l=linux-kernel&m=152043346110262&w=2 > >>>>>> > >>>>>> Co-Developed-by: Andrea Parri <andrea.parri@amarulasolutions.com> > >>>>>> Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> > >>>>>> Co-Developed-by: David Howells <dhowells@redhat.com> > >>>>>> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com> > >>>>>> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> > >>>>>> Signed-off-by: David Howells <dhowells@redhat.com> > >>>>>> 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: 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@kernel.org> > >>>>>> --- > >>>>>> include/linux/spinlock.h | 18 ++++++++++++++++++ > >>>>>> 1 file changed, 18 insertions(+) > >>>>>> > >>>>>> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > >>>>>> index 4894d322d2584..1e8a464358384 100644 > >>>>>> --- a/include/linux/spinlock.h > >>>>>> +++ b/include/linux/spinlock.h > >>>>>> @@ -380,6 +380,24 @@ 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. > >>>>>> + * > >>>>>> + * Returns: 1 if @lock is locked, 0 otherwise. > >>>>> > >>>>> Sorry, minor nit: > >>>>> s/Returns:/Return:/ > >>>>> (according to kernel-doc.rst) > >>>>> > >>>>> although I agree that "Returns:" is better. > >>>>> [I should have changed that years ago.] > >>>> > >>>> Agreed, English grammar and templates often seem to conflict. > >>>> > >>>> So should we change this comment, or are you instead proposing to add > >>>> "Returns:" as valid kernel-doc? > >>> > >>> Please change this patch to current doc syntax. > >>> Any changes to kernel-doc syntax would come later. > > > > Are you sure? > > > > $ git grep "\* Returns:" | wc -l > > 2470 > > $ git grep "\* Return:" | wc -l > > 4144 > > > > Looks like more than a third of them are already "Returns:". ;-) > > > >> Paul: I understand that you're going to do this change "in place"; please > >> let me know if I'm wrong/if you need a new submission. > > > > If Randy is certain that he would like to continue propagating > > this grammatical infelicity, sure. ;-) > > eh? > Well, Documentation/doc-guide/kernel-doc.rst says "Return:", but it appears > that it does not matter to scripts/kernel-doc -- it's just the name of a > "section" of the documentation and can be spelled any way! oh well. :) > > Acked-by: Randy Dunlap <rdunlap@infradead.org>
Applied, thank you both!
Thanx, Paul
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