On Fri, Jun 06, 2014 at 09:09:47AM -0700, James Bottomley wrote: > On Fri, 2014-06-06 at 08:55 -0700, Davidlohr Bueso wrote: > > PA-RISC's cmpxchg is not save against normal stores and the code used > > for optimistic spinning is known broken because of this. > > What about all the other identified architectures? The problem is that > unless you can do an atomic Read Modify Write on your architecture, you > have to implement our exchange primitives with locking, and that makes > you unsafe against stores We happen to be the architecture that > detected this, but I thought we agreed sparc32, metag, tile32, arc and > possibly hexagon have this problem. > > Rather than naming all the failing architectures, we probably want an > > ARCH_NO_ATOMIC_RMW The thing is, all these archs are broken beyond this particular problem, Mikulas Patocka found a number of other spots. In any case, sure I can exclude more. Although ideally someone goes do that __atomic sparse thing to flush out all this. --- Subject: locking, mutex: Disable optimistic spinning on !RMW archs For some archs a regular store does not play nice with cmpxchg(), the optimistic spinning code (and various other places not caught by this) break this assumption and make things go boom. Until something better is found, disable optimistic spinning for these archs. Cc: James.Bottomley@xxxxxxxxxxxxxxxxxxxxx Cc: davem@xxxxxxxxxxxxx Cc: james.hogan@xxxxxxxxxx Cc: cmetcalf@xxxxxxxxxx Cc: vgupta@xxxxxxxxxxxx Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> --- kernel/Kconfig.locks | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks index d2b32ac27a39..b9c132c48bf1 100644 --- a/kernel/Kconfig.locks +++ b/kernel/Kconfig.locks @@ -220,6 +220,10 @@ config INLINE_WRITE_UNLOCK_IRQRESTORE endif +config ARCH_NO_ATOMIC_RMW + def_bool y + depends on PARISC || SPARC32 || METAG_ATOMICITY_LOCK1 || (TILE && !TILEGX) || (ARC && !ARC_HAS_LLSC) + config MUTEX_SPIN_ON_OWNER def_bool y - depends on SMP && !DEBUG_MUTEXES + depends on SMP && !DEBUG_MUTEXES && !ARCH_NO_ATOMIC_RMW -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
