Date: Sun, 28 Aug 2011 11:27:44 +0200 From: Hans Petter Selasky <hselasky@freebsd.org> To: freebsd-arch@freebsd.org Cc: Andriy Gapon <avg@freebsd.org> Subject: Re: skipping locks, mutex_owned, usb Message-ID: <201108281127.44696.hselasky@freebsd.org> In-Reply-To: <4E5A099F.4060903@FreeBSD.org> References: <4E53986B.5000804@FreeBSD.org> <4E5A099F.4060903@FreeBSD.org>
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On Sunday 28 August 2011 11:25:51 Andriy Gapon wrote:
> on 23/08/2011 15:09 Andriy Gapon said the following:
> > This "XXX cludge" [sic] pattern is scattered around a few functions in
> > the ukbd code and perhaps other usb code:
> > func()
> > {
> >
> > if (!mtx_owned(&Giant)) {
> >
> > mtx_lock(&Giant);
> >
> > func();
> > mtx_unlock(&Giant);
> >
> > return;
> >
> > }
> >
> > // etc ...
> >
> > }
>
> Ohhh, nothing seems simple with the USB code:
>
> /* make sure that the BUS mutex is not locked */
> drop_bus = 0;
> while (mtx_owned(&xroot->udev->bus->bus_mtx)) {
> mtx_unlock(&xroot->udev->bus->bus_mtx);
> drop_bus++;
> }
>
> /* make sure that the transfer mutex is not locked */
> drop_xfer = 0;
> while (mtx_owned(xroot->xfer_mtx)) {
> mtx_unlock(xroot->xfer_mtx);
> drop_xfer++;
> }
>
> So many unconventional tricks.
Similar code is used in the DROP_GIANT and PICKUP_GIANT macros. You might want
to check all references to mtx_owned() in the kernel, and make a set of
exceptions for post-panic code execution.
--HPS
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