svn commit: r187978 - user/thompsa/usb/sys/dev/usb2/ethernet

[John Baldwin]

On Sunday 01 February 2009 10:36:18 pm M. Warner Losh wrote:
> In message: <20090201213749.GJ32503 at citylink.fud.org.nz>
>             Andrew Thompson <thompsa at FreeBSD.org> writes:
> : On Sun, Feb 01, 2009 at 02:28:08PM -0700, M. Warner Losh wrote:
> : > In message: <200902010650.n116obU1045871 at svn.freebsd.org>
> : >             Andrew Thompson <thompsa at FreeBSD.org> writes:
> : > : +	locked = mtx_owned(&sc->sc_mtx);
> : > : +	if (!locked)
> : > : +		AUE_LOCK(sc);
> : > 
> : > You do know this is racy, right?

Err, no it's not.  Individual threads are always "single-threaded", so whether 
or not a given thread holds a lock is actually deterministic.  This is 
perfectly fine, and is actually how recursive locks work.

> : Yea... It only get called unlocked during mii probe+attach so its fine.
> : I havnt actaully checked if its ok to hold a mutex during
> : mii_phy_probe() which would make this go away.
> 
> You hold GIANT when probe+attach, which means I think you can't
> acquire any other locks...

That's completely backwards.  :)  You can definitely acquire other locks while 
holding Giant.  What you can't do is acquire Giant while holding another 
mutex.

-- 
John Baldwin