linux-kernel - Re: Naughty ramdrives

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Date:	Fri, 8 Sep 2006 02:08:53 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>, Greg KH <greg@...ah.com>
Subject: Re: Naughty ramdrives

> So I assume udev is still madly crunching on its message backlog while
> this is happening?
>
> If so, ug.

OK. I'll let it stabilize, sorry.

> > This was noticed while investigating #4899
> > http://bugme.osdl.org/show_bug.cgi?id=4899
> > where /dev/ram0 when opened, pins module indefinitely. It seems that
> > adding ->release() which undoes
> >
> > 	inode = igrab(bdev->bd_inode);
> >
> > should do the trick. Am I right?

> Looks right.
>
> I'm not sure that igrab() is needed though.  Probably bd_openers is
> sufficient.
>
> I'm also not sure that rd_open() needs to play with bd_openers.
> fs/block_dev.c:do_open() already does that.

Maybe start with closing open/open race?
That's what drivers/char/raw.c does...
------------------------------------------------
[PATCH 1/2] rd: protect rd_bdev[] with mutex

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 drivers/block/rd.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/block/rd.c
+++ b/drivers/block/rd.c
@@ -56,6 +56,7 @@ #include <linux/buffer_head.h>		/* for i
 #include <linux/backing-dev.h>
 #include <linux/blkpg.h>
 #include <linux/writeback.h>
+#include <linux/mutex.h>
 
 #include <asm/uaccess.h>
 
@@ -63,6 +64,7 @@ #include <asm/uaccess.h>
  */
 
 static struct gendisk *rd_disks[CONFIG_BLK_DEV_RAM_COUNT];
+static DEFINE_MUTEX(rd_mutex);
 static struct block_device *rd_bdev[CONFIG_BLK_DEV_RAM_COUNT];/* Protected device data */
 static struct request_queue *rd_queue[CONFIG_BLK_DEV_RAM_COUNT];
 
@@ -343,6 +345,7 @@ static int rd_open(struct inode *inode, 
 {
 	unsigned unit = iminor(inode);
 
+	mutex_lock(&rd_mutex);
 	if (rd_bdev[unit] == NULL) {
 		struct block_device *bdev = inode->i_bdev;
 		struct address_space *mapping;
@@ -382,6 +385,7 @@ static int rd_open(struct inode *inode, 
 		gfp_mask |= __GFP_HIGH;
 		mapping_set_gfp_mask(mapping, gfp_mask);
 	}
+	mutex_unlock(&rd_mutex);
 
 	return 0;
 }

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