Date: Sun, 3 Aug 2008 18:46:38 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Ed Schouten <ed@FreeBSD.org> Cc: Perforce Change Reviews <perforce@FreeBSD.org> Subject: Re: PERFORCE change 146544 for review Message-ID: <alpine.BSF.1.10.0808031845230.18760@fledge.watson.org> In-Reply-To: <200808031737.m73HbJO8065922@repoman.freebsd.org> References: <200808031737.m73HbJO8065922@repoman.freebsd.org>
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On Sun, 3 Aug 2008, Ed Schouten wrote: > http://perforce.freebsd.org/chv.cgi?CH=146544 > > Change 146544 by ed@ed_flippo on 2008/08/03 17:36:53 > > Add a counter to store the number of null modem devices. I've seen similar constructs in lots of drivers, and it's basically an unsafe construct because the deregister is non-atomic with respect to the busy check. I wonder if, instead, we should use a mutex to protect the count, and set it to some value to deny future allocations, such as -1, once the ebusy check is past... Even that is unideal, though. Robert N M Watson Computer Laboratory University of Cambridge > > Affected files ... > > .. //depot/projects/mpsafetty/sys/dev/nmdm/nmdm.c#4 edit > > Differences ... > > ==== //depot/projects/mpsafetty/sys/dev/nmdm/nmdm.c#4 (text+ko) ==== > > @@ -93,12 +93,16 @@ > struct mtx ns_mtx; > }; > > +static int nmdm_count = 0; > + > static struct nmdmsoftc * > nmdm_alloc(unsigned long unit, struct ucred *cr) > { > struct nmdmsoftc *ns; > struct tty *tp; > > + atomic_add_acq_int(&nmdm_count, 1); > + > ns = malloc(sizeof(*ns), M_NMDM, M_WAITOK|M_ZERO); > mtx_init(&ns->ns_mtx, "nmdm", NULL, MTX_DEF); > > @@ -344,8 +348,9 @@ > break; > > case MOD_UNLOAD: > + if (nmdm_count != 0) > + return (EBUSY); > EVENTHANDLER_DEREGISTER(dev_clone, tag); > - /* XXX: track counter! */ > break; > > default: >
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