Messages in this thread |  | | Subject | Re: [PATCH v4 1/3] locking: Document the semantics of spin_is_locked() | From | Randy Dunlap <> | Date | Fri, 6 Apr 2018 14:08:16 -0700 |
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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.
Thanks.
> Thanx, Paul > >>> + * >>> + * Note that the function only tells you that the spinlock is >>> + * seen to be locked, not that it is locked on your CPU. >>> + * >>> + * Further, on CONFIG_SMP=n builds with CONFIG_DEBUG_SPINLOCK=n, >>> + * the return value is always 0 (see include/linux/spinlock_up.h). >>> + * Therefore you should not rely heavily on the return value. >>> + */ >>> static __always_inline int spin_is_locked(spinlock_t *lock) >>> { >>> return raw_spin_is_locked(&lock->rlock); >>> >> >> >> -- >> ~Randy >> >
-- ~Randy
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