From: Michael Ellerman <mpe@ellerman.id.au>
To: Peter Zijlstra <peterz@infradead.org>, Boqun Feng <boqun.feng@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v3] powerpc: spinlock: Fix spin_unlock_wait()
Date: Thu, 09 Jun 2016 22:23:28 +1000 [thread overview]
Message-ID: <1465475008.16363.1.camel@ellerman.id.au> (raw)
In-Reply-To: <20160608135903.GT30154@twins.programming.kicks-ass.net>
On Wed, 2016-06-08 at 15:59 +0200, Peter Zijlstra wrote:
> On Wed, Jun 08, 2016 at 11:49:20PM +1000, Michael Ellerman wrote:
>
> > > Ok; what tree does this go in? I have this dependent series which I'd
> > > like to get sorted and merged somewhere.
> >
> > Ah sorry, I didn't realise. I was going to put it in my next (which doesn't
> > exist yet but hopefully will early next week).
> >
> > I'll make a topic branch with just that commit based on rc2 or rc3?
>
> Works for me; thanks!
Unfortunately the patch isn't 100%.
It's causing some of my machines to lock up hard, which isn't surprising when
you look at the generated code for the non-atomic spin loop:
c00000000009af48: 7c 21 0b 78 mr r1,r1 # HMT_LOW
c00000000009af4c: 40 9e ff fc bne cr7,c00000000009af48 <.do_exit+0x6d8>
Which is a spin loop waiting for a result in cr7, but with no comparison.
The problem seems to be that we did:
@@ -184,7 +184,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
if (arch_spin_value_unlocked(lock_val))
goto out;
- while (lock->slock) {
+ while (!arch_spin_value_unlocked(*lock)) {
HMT_low();
if (SHARED_PROCESSOR)
__spin_yield(lock);
Which seems to be hiding the fact that lock->slock is volatile from the
compiler, even though arch_spin_value_unlocked() is inline. Not sure if that's
our bug or gcc's.
Will sleep on it.
cheers
next prev parent reply other threads:[~2016-06-09 12:23 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-06 11:42 [PATCH v3] powerpc: spinlock: Fix spin_unlock_wait() Michael Ellerman
2016-06-06 11:56 ` Peter Zijlstra
2016-06-06 12:17 ` Michael Ellerman
2016-06-06 14:46 ` Peter Zijlstra
2016-06-08 11:20 ` Michael Ellerman
2016-06-08 12:35 ` Peter Zijlstra
2016-06-08 13:49 ` Michael Ellerman
2016-06-08 13:59 ` Peter Zijlstra
2016-06-09 12:23 ` Michael Ellerman [this message]
2016-06-09 17:25 ` Boqun Feng
2016-06-10 3:06 ` Boqun Feng
2016-06-09 17:50 ` Peter Zijlstra
2016-06-10 0:57 ` Michael Ellerman
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