Date: Mon, 2 Feb 2009 08:36:28 -0500 From: John Baldwin <jhb@freebsd.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: src-committers@freebsd.org, thompsa@freebsd.org, svn-src-user@freebsd.org Subject: Re: svn commit: r187978 - user/thompsa/usb/sys/dev/usb2/ethernet Message-ID: <200902020836.28882.jhb@freebsd.org> In-Reply-To: <20090201.203618.1640016624.imp@bsdimp.com> References: <200902010650.n116obU1045871@svn.freebsd.org> <20090201213749.GJ32503@citylink.fud.org.nz> <20090201.203618.1640016624.imp@bsdimp.com>
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On Sunday 01 February 2009 10:36:18 pm M. Warner Losh wrote: > In message: <20090201213749.GJ32503@citylink.fud.org.nz> > Andrew Thompson <thompsa@FreeBSD.org> writes: > : On Sun, Feb 01, 2009 at 02:28:08PM -0700, M. Warner Losh wrote: > : > In message: <200902010650.n116obU1045871@svn.freebsd.org> > : > Andrew Thompson <thompsa@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
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