Re: [PATCH] locking/pvqspinlock: Correct the type of "old" variable in pv_kick_node()

[Waiman Long]

On 7/22/24 02:54, maobibo wrote:
> Uros,
>
> Sorry for late reply because of weekend time. This modification works 
> well for me.
>
> In later I want to define pv_node::state as int type on LoongArch 
> because there is only int32/int64 cmpxchg is better supported on the 
> system, however that is another issue.

I thought about changing pv_node::state to int, but that requires 
changing the pv_wait() call to use int too. That doesn't work because 
pv_wait() is also used to monitor the state of the lock byte of the 
qspinlock. In essence, we can't use pvqspinlock if 8-bit cmpxchg isn't 
supported.

Cheers,
Longman

> Tested-by:Bibo Mao <maobibo@xxxxxxxxxxx>
>
> On 2024/7/22 上午12:45, Uros Bizjak wrote:
> > "enum vcpu_state" is not compatible with "u8" type for all targets,
> > resulting in:
> >
> > error: initialization of 'u8 *' {aka 'unsigned char *'} from 
> > incompatible pointer type 'enum vcpu_state *'
> >
> > for LoongArch. Correct the type of "old" variable to "u8".
> >
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Cc: Waiman Long <longman@xxxxxxxxxx>
> > Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> > Fixes: fea0e1820b51 ("locking/pvqspinlock: Use try_cmpxchg() in 
> > qspinlock_paravirt.h")
> > Reported-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> > Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> > Closes: 
> > https://lore.kernel.org/lkml/20240719024010.3296488-1-maobibo@xxxxxxxxxxx/
> > ---
> >   kernel/locking/qspinlock_paravirt.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/locking/qspinlock_paravirt.h 
> > b/kernel/locking/qspinlock_paravirt.h
> > index f5a36e67b593..ac2e22502741 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock 
> > *node, struct mcs_spinlock *prev)
> >   static void pv_kick_node(struct qspinlock *lock, struct 
> > mcs_spinlock *node)
> >   {
> >       struct pv_node *pn = (struct pv_node *)node;
> > -    enum vcpu_state old = vcpu_halted;
> > +    u8 old = vcpu_halted;
> >       /*
> >        * If the vCPU is indeed halted, advance its state to match 
> > that of
> >        * pv_wait_node(). If OTOH this fails, the vCPU was running and 
> > will