RE: [PATCH] vfio/platform: Replace spin_lock_irqsave by spin_lock in hard IRQ
From: Song Bao Hua (Barry Song)
Date: Tue Oct 13 2020 - 20:15:19 EST
> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Wednesday, October 14, 2020 10:32 AM
> To: tiantao (H) <tiantao6@xxxxxxxxxxxxx>
> Cc: eric.auger@xxxxxxxxxx; cohuck@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Song Bao Hua (Barry Song)
> <song.bao.hua@xxxxxxxxxxxxx>; Linuxarm <linuxarm@xxxxxxxxxx>
> Subject: Re: [PATCH] vfio/platform: Replace spin_lock_irqsave by spin_lock in
> hard IRQ
>
> On Tue, 13 Oct 2020 10:00:58 +0800
> Tian Tao <tiantao6@xxxxxxxxxxxxx> wrote:
>
> > It is redundant to do irqsave and irqrestore in hardIRQ context.
>
> But this function is also called from non-IRQ context. Thanks,
It seems you mean
vfio_platform_set_irqs_ioctl() ->
vfio_platform_set_irq_trigger ->
handler() ?
so, will it be better to move the irqsave out of the vfio_automasked_irq_handler()
and put it to where the function is called in non-IRQ context?
I mean:
irqhandler()
{
spin_lock() //without irqsave
spin_unlock()
}
Non-irq context which is calling this handler:
irqsave();
irqhandler();
irqrestore();
Anyway, if it is called in IRQ context, it is redundant to do irqsave.
>
> Alex
>
> > Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
> > ---
> > drivers/vfio/platform/vfio_platform_irq.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vfio/platform/vfio_platform_irq.c
> b/drivers/vfio/platform/vfio_platform_irq.c
> > index c5b09ec..24fd6c5 100644
> > --- a/drivers/vfio/platform/vfio_platform_irq.c
> > +++ b/drivers/vfio/platform/vfio_platform_irq.c
> > @@ -139,10 +139,9 @@ static int vfio_platform_set_irq_unmask(struct
> vfio_platform_device *vdev,
> > static irqreturn_t vfio_automasked_irq_handler(int irq, void *dev_id)
> > {
> > struct vfio_platform_irq *irq_ctx = dev_id;
> > - unsigned long flags;
> > int ret = IRQ_NONE;
> >
> > - spin_lock_irqsave(&irq_ctx->lock, flags);
> > + spin_lock(&irq_ctx->lock);
> >
> > if (!irq_ctx->masked) {
> > ret = IRQ_HANDLED;
> > @@ -152,7 +151,7 @@ static irqreturn_t vfio_automasked_irq_handler(int
> irq, void *dev_id)
> > irq_ctx->masked = true;
> > }
> >
> > - spin_unlock_irqrestore(&irq_ctx->lock, flags);
> > + spin_unlock(&irq_ctx->lock);
> >
> > if (ret == IRQ_HANDLED)
> > eventfd_signal(irq_ctx->trigger, 1);
Thanks
Barry