On 10/11/2009 3:45 PM, John Kacur wrote:
> Locking in ch_open is covered by the spin_lock, it serializes the calls
> to idr_find and scsi_device_get. The BKL appears redundant to me here.
Superficially this looks OK (i.e. no race with driver init in general).
But I do wonder if there isn't already a race condition possible with
the current code, between ch_probe and the file operations. ch_probe
makes a scsi_changer instance available in the IDR and creates the
corresponding character device file _before_ the scsi_changer instance
is fully initialized.
(Full quote follows for lsml)
> From b385c85bb5c2579e542cfe55475b729325eb65e1 Mon Sep 17 00:00:00 2001
> From: John Kacur <jkacur@xxxxxxxxxx>
> Date: Sun, 11 Oct 2009 13:06:54 +0200
> Subject: [PATCH] drivers/scsi/ch.c: Remove BKL in ch_open
>
> Everything in ch_open is covered by a spin_lock, so the lock_kernel is redundant
> Remove it.
>
> Signed-off-by: John Kacur <jkacur@xxxxxxxxxx>
> ---
> drivers/scsi/ch.c | 5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/scsi/ch.c b/drivers/scsi/ch.c
> index fe11c1d..4ba8b67 100644
> --- a/drivers/scsi/ch.c
> +++ b/drivers/scsi/ch.c
> @@ -579,19 +579,16 @@ ch_open(struct inode *inode, struct file *file)
> scsi_changer *ch;
> int minor = iminor(inode);
>
> - lock_kernel();
> spin_lock(&ch_index_lock);
> ch = idr_find(&ch_index_idr, minor);
>
> if (NULL == ch || scsi_device_get(ch->device)) {
> spin_unlock(&ch_index_lock);
> - unlock_kernel();
> return -ENXIO;
> }
> + file->private_data = ch;
> spin_unlock(&ch_index_lock);
>
> - file->private_data = ch;
> - unlock_kernel();
> return 0;
> }
>
--
Stefan Richter
-=====-==--= =-=- -==--
http://arcgraph.de/sr/
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