On 09/29/2016 12:23 PM, Christian Borntraeger wrote:

On 09/29/2016 12:10 PM, Peter Zijlstra wrote:

quoted

On Thu, Jul 21, 2016 at 07:45:10AM -0400, Pan Xinhui wrote:

quoted

change from v2:
	no code change, fix typos, update some comments

change from v1:
	a simplier definition of default vcpu_is_preempted
	skip mahcine type check on ppc, and add config. remove dedicated macro.
	add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. 
	add more comments
	thanks boqun and Peter's suggestion.

This patch set aims to fix lock holder preemption issues.

So I really like the concept, but I would also really like to see
support for more hypervisors included before we can move forward with
this.

Please consider s390 and (x86/arm) KVM. Once we have a few, more can
follow later, but I think its important to not only have PPC support for
this.

Actually the s390 preemted check via sigp sense running  is available for
all hypervisors (z/VM, LPAR and KVM) which implies everywhere as you can no
longer buy s390 systems without LPAR.

As Heiko already pointed out we could simply use a small inline function
that calls cpu_is_preempted from arch/s390/lib/spinlock (or smp_vcpu_scheduled from smp.c)

Maybe something like
(untested and just pasted, so white space damaged)

diff --git a/arch/s390/include/asm/spinlock.h b/arch/s390/include/asm/spinlock.h
index 63ebf37..6e82986 100644
--- a/arch/s390/include/asm/spinlock.h
+++ b/arch/s390/include/asm/spinlock.h

@@ -21,6 +21,13 @@ _raw_compare_and_swap(unsigned int *lock, unsigned int old, unsigned int new)
        return __sync_bool_compare_and_swap(lock, old, new);
 }
 
+int arch_vcpu_is_preempted(int cpu);
+#define vcpu_is_preempted cpu_is_preempted
+static inline bool cpu_is_preempted(int cpu)
+{
+       return arch_vcpu_is_preempted(cpu);
+}
+
 /*
  * Simple spin lock operations.  There are two variants, one clears IRQ's
  * on the local processor, one does not.

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index e5f50a7..260d179 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c

@@ -37,7 +37,7 @@ static inline void _raw_compare_and_delay(unsigned int *lock, unsigned int old)
        asm(".insn rsy,0xeb0000000022,%0,0,%1" : : "d" (old), "Q" (*lock));
 }
 
-static inline int cpu_is_preempted(int cpu)
+int arch_vcpu_is_preempted(int cpu)
 {
        if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
                return 0;

@@ -45,6 +45,7 @@ static inline int cpu_is_preempted(int cpu)
                return 0;
        return 1;
 }
+EXPORT_SYMBOL(arch_vcpu_is_preempted);
 
 void arch_spin_lock_wait(arch_spinlock_t *lp)
 {

If ok I can respin into a proper patch.