Messages in this thread | | | Date | Thu, 12 Nov 2015 06:32:31 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH] mips: Fix arch_spin_unlock() |
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On Thu, Nov 12, 2015 at 01:31:23PM +0100, Peter Zijlstra wrote: > Hi > > I think the MIPS arch_spin_unlock() is borken. > > spin_unlock() must have RELEASE semantics, these require that no LOADs > nor STOREs leak out from the critical section. > > >From what I know MIPS has a relaxed memory model which allows reads to > pass stores, and as implemented arch_spin_unlock() only issues a wmb > which doesn't order prior reads vs later stores. > > Therefore upgrade the wmb() to smp_mb(). > > (Also, why the unconditional wmb, as opposed to smp_wmb() ?)
One guess is that they want to order I/O accesses within the critical section?
Thanx, Paul
> Maybe-Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h > index 40196bebe849..b2ca13f06152 100644 > --- a/arch/mips/include/asm/spinlock.h > +++ b/arch/mips/include/asm/spinlock.h > @@ -140,7 +140,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) > static inline void arch_spin_unlock(arch_spinlock_t *lock) > { > unsigned int serving_now = lock->h.serving_now + 1; > - wmb(); > + smp_mb(); > lock->h.serving_now = (u16)serving_now; > nudge_writes(); > } >
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