Messages in this thread Patch in this message | | | Date | Mon, 26 Mar 2018 16:14:36 +0200 | From | Andrea Parri <> | Subject | Re: [PATCH for-4.17 1/2] arm64: Remove smp_mb() from arch_spin_is_locked() |
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On Mon, Mar 26, 2018 at 11:57:05AM +0100, Will Deacon wrote: > On Mon, Mar 26, 2018 at 12:37:21PM +0200, Andrea Parri wrote: > > Commit 38b850a73034f ("arm64: spinlock: order spin_{is_locked,unlock_wait} > > against local locks") added an smp_mb() to arch_spin_is_locked(), in order > > "to ensure that the lock value is always loaded after any other locks have > > been taken by the current CPU", and reported one example (the "insane case" > > in ipc/sem.c) relying on such guarantee. > > > > It is however understood (and not documented) that spin_is_locked() is not > > required to ensure such an ordering guarantee, guarantee that is currently > > _not_ provided by all implementations/architectures, and that callers rely- > > ing on such ordering should instead insert suitable memory barriers before > > acting on the result of spin_is_locked(). > > > > Following a recent auditing[1] of the callsites of {,raw_}spin_is_locked() > > revealing that none of these callers are relying on the ordering guarantee > > anymore, this commit removes the leading smp_mb() from this primitive thus > > effectively reverting 38b850a73034f. > > > > [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 > > What is patch 2/2 in this series? I couldn't find it in the archive.
2/2 is this change for powerpc:
https://marc.info/?l=linux-kernel&m=152206068707522&w=2
> > Assuming that patch doesn't do it, please can you remove the comment > about spin_is_locked from mutex_is_locked?
I ended up with the patch below but I suspect that it's not what you had in mind; please let me know if you'd like me to add it into this series.
> > Also -- does this mean we can kill the #ifndef queued_spin_is_locked > guards in asm-generic/qspinlock.h?
I don't see why arch may want to override that definition (maybe lack of imagination?); please let me know if you'd like to see the #ifndef gone.
Andrea
--- From 1b77a9a70823620f1c98e43453edf5707d02074e Mon Sep 17 00:00:00 2001 From: Andrea Parri <andrea.parri@amarulasolutions.com> Date: Mon, 26 Mar 2018 15:03:58 +0200 Subject: [PATCH] mutex: Remove the comment about spin_is_locked() from mutex_is_locked()
Still true/valid, but not particularly useful [IMO].
Suggested-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com> --- include/linux/mutex.h | 3 --- 1 file changed, 3 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h index cb3bbed4e6339..9921822c51585 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -147,9 +147,6 @@ extern void __mutex_init(struct mutex *lock, const char *name, */ static inline bool mutex_is_locked(struct mutex *lock) { - /* - * XXX think about spin_is_locked - */ return __mutex_owner(lock) != NULL; } -- 2.7.4
> > Will
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