Subject: Re: [PATCH v3 03/17] powerpc: Add PFO support to the VIO bus

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 01 May 2012 13:06:43 +1000

Hrm... I don't like that much:

> +	if (op->timeout)
> +		deadline = jiffies + msecs_to_jiffies(op->timeout);
> +
> +	while (true) {
> +		hret = plpar_hcall_norets(H_COP, op->flags,
> +				vdev->resource_id,
> +				op->in, op->inlen, op->out,
> +				op->outlen, op->csbcpb);
> +
> +		if (hret == H_SUCCESS ||
> +		    (hret != H_NOT_ENOUGH_RESOURCES &&
> +		     hret != H_BUSY && hret != H_RESOURCE) ||
> +		    (op->timeout && time_after(deadline, jiffies)))
> +			break;
> +
> +		dev_dbg(dev, "%s: hcall ret(%ld), retrying.\n", __func__, hret);
> +	}
> +

Is this meant to be called in atomic context ? If not, maybe it should
at the very least do a cond_resched() ?

Else, what about ceding the processor ? Or at the very least reducing
the thread priority for a bit ?

Shouldn't we also enforce to always have a timeout ? IE. Something like
30s or so if nothing specified to avoid having the kernel just hard
lock...

In general I don't like that sort of synchronous code, I'd rather return
the busy status up the chain which gives a chance to the caller to take
more appropriate measures depending on what it's doing, but that really
depends what you use that synchronous call for. I suppose if it's for
configuration type operations, it's ok...

Cheers,
Ben.