On Fri, 8 Sep 2006 02:08:53 +0400
Alexey Dobriyan <[email protected]> wrote:
> > 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.
You shouldn't have to.
> > > 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 <[email protected]>
> ---
>
> 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);
This could be static to rd_open().
> 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);
I suspect that we've inherited enough locking from the caller to not need
this. That's if fs/block_dev.c:do_open() is the only caller. Not sure if
that's true if someone goes and partitions a ramdisk (is that possible?).
All this gendisk/blockdev/contains/partitions/bd_inode stuff is quite
ghastly. Every six months I spend long enough staring at it to
half-understand it and then promptly forget how it all works.
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