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

Hans J. Koch
2011-08-09T18:54:03Z

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>
---
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