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

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Date:	Tue, 9 Aug 2011 20:53:41 +0200
From:	"Hans J. Koch" <hjk@...sjkoch.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Chris Wright <chrisw@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Anthony Foiani <anthony.foiani@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uio/gen-pci: don't enable interrupts in ISR

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@...sjkoch.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@...hat.com>
Cc: Chris Wright <chrisw@...hat.com>
Cc: Jesse Barnes <jbarnes@...tuousgeek.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Anthony Foiani <anthony.foiani@...il.com>
Reported-by: Anthony Foiani <anthony.foiani@...il.com>
Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Hans J. Koch <hjk@...sjkoch.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@...hat.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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