Re: [PATCH] uio/gen-pci: don't enable interrupts in ISR

Michael S. Tsirkin
2011-08-10T08:40:17Z

On Tue, Aug 09, 2011 at 08:53:41PM +0200, Hans J. Koch wrote:
> On Tue, Aug 09, 2011 at 02:37:43PM +0300, Michael S. Tsirkin wrote:
> > >
> > > Should I hack up a patch to remove the lock, or do you have anything in your
> > > pipeline?
> >
> >
> > Please do.
> >
>
> Here it is:
>
> Greg (and anyone else...), you can also pull this from branch "uio-for-greg" from
>
> git://hansjkoch.de/git/linux-hjk
>
>
> >From ff74627ade002d40fe1f902b7aadab8b1f15f889 Mon Sep 17 00:00:00 2001
> From: "Hans J. Koch" <hjk@hansjkoch.de>
> Date: Tue, 9 Aug 2011 20:34:31 +0200
> Subject: [PATCH] uio: uio_pci_generic: Remove useless spin_lock
>
> The spin_lock in uio_pci_generic.c is only used in the interrupt
> handler, which cannot be executed twice at the same time.
> That makes the lock rather pointless. This patch removes it.
>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Chris Wright <chrisw@redhat.com>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Anthony Foiani <anthony.foiani@gmail.com>
> Reported-by: Anthony Foiani <anthony.foiani@gmail.com>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Hans J. Koch <hjk@hansjkoch.de>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

I also suggest this for the stable trees.

> ---
> drivers/uio/uio_pci_generic.c | 5 -----
> 1 files changed, 0 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
> index fc22e1e..02bd47b 100644
> --- a/drivers/uio/uio_pci_generic.c
> +++ b/drivers/uio/uio_pci_generic.c
> @@ -24,7 +24,6 @@
> #include <linux/pci.h>
> #include <linux/slab.h>
> #include <linux/uio_driver.h>
> -#include <linux/spinlock.h>
>
> #define DRIVER_VERSION "0.01.0"
> #define DRIVER_AUTHOR "Michael S. Tsirkin <mst@redhat.com>"
> @@ -33,7 +32,6 @@
> struct uio_pci_generic_dev {
> struct uio_info info;
> struct pci_dev *pdev;
> - spinlock_t lock; /* guards command register accesses */
> };
>
> static inline struct uio_pci_generic_dev *
> @@ -57,7 +55,6 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
> BUILD_BUG_ON(PCI_COMMAND % 4);
> BUILD_BUG_ON(PCI_COMMAND + 2 != PCI_STATUS);
>
> - spin_lock_irq(&gdev->lock);
> pci_block_user_cfg_access(pdev);
>
> /* Read both command and status registers in a single 32-bit operation.
> @@ -83,7 +80,6 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
> done:
>
> pci_unblock_user_cfg_access(pdev);
> - spin_unlock_irq(&gdev->lock);
> return ret;
> }
>
> @@ -158,7 +154,6 @@ static int __devinit probe(struct pci_dev *pdev,
> gdev->info.irq_flags = IRQF_SHARED;
> gdev->info.handler = irqhandler;
> gdev->pdev = pdev;
> - spin_lock_init(&gdev->lock);
>
> if (uio_register_device(&pdev->dev, &gdev->info))
> goto err_register;
> --
> 1.7.5.4