netdev - Re: Remaining BKL users, what to do

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Date:	Fri, 17 Sep 2010 20:46:10 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	"codalist@...a.cs.cmu.edu" <codalist@...a.cs.cmu.edu>,
	"autofs@...ux.kernel.org" <autofs@...ux.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Christoph Hellwig <hch@...radead.org>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Petr Vandrovec <vandrove@...cvut.cz>,
	Anders Larsen <al@...rsen.net>, Jan Kara <jack@...e.cz>,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Ingo Molnar <mingo@...e.hu>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Samuel Ortiz <samuel@...tiz.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Hendry <andrew.hendry@...il.com>
Subject: Re: Remaining BKL users, what to do

On Thursday 16 September 2010 20:32:36 Jens Axboe wrote:
> On 2010-09-16 16:49, Steven Rostedt wrote:
> > Git blame shows this to be your code (copied from block/blktrace.c from
> > years past).
> > 
> > Is the lock_kernel() needed here? (although Arnd did add it in 62c2a7d9)
> 
> It isn't, it can be removed.

Ok, I queued up this patch now. Thanks!

	Arnd
---
Subject: [PATCH] blktrace: remove the big kernel lock

According to Jens, this code does not need the BKL at all,
it is sufficiently serialized by bd_mutex.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Cc: Jens Axboe <jaxboe@...ionio.com>
Cc: Steven Rostedt <rostedt@...dmis.org>

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 959f8d6..5328e87 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -23,7 +23,6 @@
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/debugfs.h>
-#include <linux/smp_lock.h>
 #include <linux/time.h>
 #include <linux/uaccess.h>
 
@@ -639,7 +638,6 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
 	if (!q)
 		return -ENXIO;
 
-	lock_kernel();
 	mutex_lock(&bdev->bd_mutex);
 
 	switch (cmd) {
@@ -667,7 +665,6 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
 	}
 
 	mutex_unlock(&bdev->bd_mutex);
-	unlock_kernel();
 	return ret;
 }
 
@@ -1652,10 +1649,9 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
 	struct block_device *bdev;
 	ssize_t ret = -ENXIO;
 
-	lock_kernel();
 	bdev = bdget(part_devt(p));
 	if (bdev == NULL)
-		goto out_unlock_kernel;
+		goto out;
 
 	q = blk_trace_get_queue(bdev);
 	if (q == NULL)
@@ -1683,8 +1679,7 @@ out_unlock_bdev:
 	mutex_unlock(&bdev->bd_mutex);
 out_bdput:
 	bdput(bdev);
-out_unlock_kernel:
-	unlock_kernel();
+out:
 	return ret;
 }
 
@@ -1714,11 +1709,10 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
 
 	ret = -ENXIO;
 
-	lock_kernel();
 	p = dev_to_part(dev);
 	bdev = bdget(part_devt(p));
 	if (bdev == NULL)
-		goto out_unlock_kernel;
+		goto out;
 
 	q = blk_trace_get_queue(bdev);
 	if (q == NULL)
@@ -1753,8 +1747,6 @@ out_unlock_bdev:
 	mutex_unlock(&bdev->bd_mutex);
 out_bdput:
 	bdput(bdev);
-out_unlock_kernel:
-	unlock_kernel();
 out:
 	return ret ? ret : count;
 }
--
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