lkml.org 
[lkml]   [2018]   [Apr]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v4 1/3] locking: Document the semantics of spin_is_locked()
    From
    Date
    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>

    Thanks.

    --
    ~Randy

    \
     
     \ /
      Last update: 2018-04-08 23:34    [W:2.412 / U:0.904 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site