On Wed, May 23, 2012 at 10:44 PM, loody <miloody@xxxxxxxxx> wrote:
> take multi-core system for example, it is possible your completion
> handler execute at the same time, except you add a spin lock for
> activating your completion function.
>
That's the reason I'm asking in first place.
But if that is true, then it seems to me some drivers wouldn't be
working (unlikely, right?)
You can take a look at pwc completion for instance:
static void pwc_isoc_handler(struct urb *urb)
{
[snip]
if (pdev->fill_buf == NULL)
pdev->fill_buf = pwc_get_next_fill_buf(pdev);
---
As you can see, there is no lock here (though there is lock
to get the next fill_buf) and pdev->fill_buf is obviously not local.
On the other hand, em28xx has a tighter locking scheme:
static void em28xx_irq_callback(struct urb *urb)
{
[snip]
/* Copy data from URB */
spin_lock(&dev->slock);
dev->isoc_ctl.isoc_copy(dev, urb);
spin_unlock(&dev->slock);
---
Currently, I'm running a three core (yes three!) streaming at a high
rate and I'm following pwc locking (per queue). So far no races found (phew).
As a sidenote, em28xx locking can be improved for a very simple
reason: it's locking code instead of data.
Unfortunately, I don't own that hardware to fix and test such a patch.
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