[PATCH v2] scsi: sg: Avoid race in error handling & drop bogus warn

[Bart Van Assche]

On 4/1/24 03:03, Alexander Wetzel wrote:
> commit 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race")
> introduced an incorrect WARN_ON_ONCE() and missed a sequence where
> sg_device_destroy() was used after scsi_device_put().

Isn't that too negative? I think that the WARN_ON_ONCE() mentioned above
has proven to be useful: it helped to catch a bug.

> sg_device_destroy() is accessing the parent scsi_device request_queue which
> will already be set to NULL when the preceding call to scsi_device_put()
> removed the last reference to the parent scsi_device.
> 
> Drop the incorrect WARN_ON_ONCE() - allowing more than one concurrent
> access to the sg device - and make sure sg_device_destroy() is not used
> after scsi_device_put() in the error handling.
> 
> Link: https://lore.kernel.org/all/5375B275-D137-4D5F-BE25-6AF8ACAE41EF@linux.ibm.com
> Fixes: 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race")

The "goto sg_put" removed by this patch was introduced by commit
cc833acbee9d ("sg: O_EXCL and other lock handling"). Since the latter
commit is older than the one mentioned above, shouldn't the Fixes tag
refer to the latter commit?

> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 386981c6976a..833c9277419b 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -372,8 +372,9 @@ sg_open(struct inode *inode, struct file *filp)
>   error_out:
>   	scsi_autopm_put_device(sdp->device);
>   sdp_put:
> +	kref_put(&sdp->d_ref, sg_device_destroy);
>   	scsi_device_put(sdp->device);
> -	goto sg_put;
> +	return retval;
>   }

Please add a comment above "return retval" that explains which code will
drop the sg reference.

Thanks,

Bart.