Date: Fri, 22 May 2009 11:20:31 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@freebsd.org> Cc: Scott Long <scottl@samsco.org>, src-committers@freebsd.org, John Baldwin <jhb@freebsd.org>, svn-src-all@freebsd.org, rwatson@freebsd.org, svn-src-head@freebsd.org, "M. Warner Losh" <imp@bsdimp.com> Subject: Re: svn commit: r192535 - head/sys/kern Message-ID: <20090522082031.GY1927@deviant.kiev.zoral.com.ua> In-Reply-To: <3bbf2fe10905211511g53defb6cmac45fc2469cc64f@mail.gmail.com> References: <3bbf2fe10905210629p46c7a204v6863aaba77354462@mail.gmail.com> <20090521.094100.70797067.imp@bsdimp.com> <4A157919.7040103@samsco.org> <200905211211.00168.jhb@freebsd.org> <20090521161535.GQ1927@deviant.kiev.zoral.com.ua> <4A157FF3.8020408@samsco.org> <20090521163846.GT1927@deviant.kiev.zoral.com.ua> <3bbf2fe10905211005m350dc4d1yed6dc1b79f1603d9@mail.gmail.com> <20090521194243.GW1927@deviant.kiev.zoral.com.ua> <3bbf2fe10905211511g53defb6cmac45fc2469cc64f@mail.gmail.com>
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On Fri, May 22, 2009 at 12:11:02AM +0200, Attilio Rao wrote:
> 2009/5/21 Kostik Belousov <kostikbel@gmail.com>:
> > On Thu, May 21, 2009 at 07:05:17PM +0200, Attilio Rao wrote:
> >> 2009/5/21 Kostik Belousov <kostikbel@gmail.com>:
> >> > On Thu, May 21, 2009 at 09:23:15AM -0700, Scott Long wrote:
> >> >> Kostik Belousov wrote:
> >> >> >We do have the KPI for the callers that cannot drop the locks and =
need
> >> >> >to do destroy_dev, destroy_dev_sched(9).
> >> >>
> >> >> Good to know, I'll look at destroy_dev_sched(). =9AI'd rather not h=
ave to
> >> >> roll my own decoupled version. =9AAnd I understand the argument abo=
ut
> >> >> destroy_dev being a drain point for the API. =9AHowever, what about
> >> >> create_dev()? =9AMaking that non-blocking would help a lot.
> >> >
> >> > create_dev() can be made non-blocking, and this is the first argumen=
t pro
> >> > Attilio patch.
> >> >
> >> > From the quick look, all that is needed is to replace M_WAITOK with
> >> > M_NOWAIT inside prep_cdevsw() and devfs_alloc(). Untested patch belo=
w.
> >> >
> >> > diff --git a/sys/fs/devfs/devfs_devs.c b/sys/fs/devfs/devfs_devs.c
> >> > index 4041911..f470ee8 100644
> >> > --- a/sys/fs/devfs/devfs_devs.c
> >> > +++ b/sys/fs/devfs/devfs_devs.c
> >> > @@ -120,7 +120,7 @@ devfs_alloc(void)
> >> > =9A =9A =9A =9Astruct cdev *cdev;
> >> > =9A =9A =9A =9Astruct timespec ts;
> >> >
> >> > - =9A =9A =9A cdp =3D malloc(sizeof *cdp, M_CDEVP, M_USE_RESERVE | M=
_ZERO | M_WAITOK);
> >> > + =9A =9A =9A cdp =3D malloc(sizeof *cdp, M_CDEVP, M_USE_RESERVE | M=
_ZERO | M_NOWAIT);
> >> >
> >> > =9A =9A =9A =9Acdp->cdp_dirents =3D &cdp->cdp_dirent0;
> >> > =9A =9A =9A =9Acdp->cdp_dirent0 =3D NULL;
> >> > diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
> >> > index 284f482..acdd44a 100644
> >> > --- a/sys/kern/kern_conf.c
> >> > +++ b/sys/kern/kern_conf.c
> >> > @@ -559,7 +559,7 @@ prep_cdevsw(struct cdevsw *devsw)
> >> > =9A =9A =9A =9A =9A =9A =9A =9Areturn;
> >> > =9A =9A =9A =9Aif (devsw->d_flags & D_NEEDGIANT) {
> >> > =9A =9A =9A =9A =9A =9A =9A =9Adev_unlock();
> >> > - =9A =9A =9A =9A =9A =9A =9A dsw2 =3D malloc(sizeof *dsw2, M_DEVT, =
M_WAITOK);
> >> > + =9A =9A =9A =9A =9A =9A =9A dsw2 =3D malloc(sizeof *dsw2, M_DEVT, =
M_NOWAIT);
> >> > =9A =9A =9A =9A =9A =9A =9A =9Adev_lock();
> >> > =9A =9A =9A =9A} else
> >> > =9A =9A =9A =9A =9A =9A =9A =9Adsw2 =3D NULL;
> >>
> >> You need to check return values here if it returns NULL.
> >>
> >> IMHO, having a non-sleepable version of destroy_dev(), create_dev()
> >> and such would be ideal.
> >> Ideally, we should resolve all the sleeping point and do the conversio=
n.
> >> I'm unable to check the code right now.
> >
> > Sure. Something like this.
> >
>=20
> At this point I wonder what's the purpose of maintaining the sleeping
> version for such functions?
They cannot fail, thus behaving in the way that all present consumers
of the function expect.
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