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


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