Re: [PATCH 7/7] accel/qaic: Add QAIC_DETACH_SLICE_BO IOCTL

[Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>]

On Fri, Sep 01, 2023 at 11:22:47AM -0600, Jeffrey Hugo wrote:
> From: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
> 
> Once a BO is attached with slicing configuration that BO can only be used
> for that particular setting. With this new feature user can detach slicing
> configuration off an already sliced BO and attach new slicing configuration
> using QAIC_ATTACH_SLICE_BO.
> 
> This will support BO recycling.
> 
> detach_slice_bo() detaches slicing configuration from a BO. This new
> helper function can also be used in release_dbc() as we are doing the
> exact same thing.
> 
> Signed-off-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
> Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
> [jhugo: add documentation for new ioctl]
> Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
<snip>

> +	/* Check if BO is committed to H/W for DMA */
> +	spin_lock_irqsave(&dbc->xfer_lock, flags);
> +	if (bo->queued) {
> +		spin_unlock_irqrestore(&dbc->xfer_lock, flags);
> +		ret = -EBUSY;
> +		goto unlock_ch_srcu;
> +	}
> +	spin_unlock_irqrestore(&dbc->xfer_lock, flags);

This looks like race condition. If some other thread will take the xfer_lock
and set bo->queued (HERE just after _unlock())  we will not return -EBUSY.
Something seems to be missing here or xfer_lock is not needed to protect
bo->queued.

Regards
Stanislaw