Date: Fri, 22 May 2009 00:11:02 +0200 From: Attilio Rao <attilio@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> 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: <3bbf2fe10905211511g53defb6cmac45fc2469cc64f@mail.gmail.com> In-Reply-To: <20090521194243.GW1927@deviant.kiev.zoral.com.ua> 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>
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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 ne=
ed
>> >> >to do destroy_dev, destroy_dev_sched(9).
>> >>
>> >> Good to know, I'll look at destroy_dev_sched(). =C2=A0I'd rather not =
have to
>> >> roll my own decoupled version. =C2=A0And I understand the argument ab=
out
>> >> destroy_dev being a drain point for the API. =C2=A0However, what abou=
t
>> >> create_dev()? =C2=A0Making that non-blocking would help a lot.
>> >
>> > create_dev() can be made non-blocking, and this is the first argument =
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 below.
>> >
>> > 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)
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0struct cdev *cdev;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0struct timespec ts;
>> >
>> > - =C2=A0 =C2=A0 =C2=A0 cdp =3D malloc(sizeof *cdp, M_CDEVP, M_USE_RESE=
RVE | M_ZERO | M_WAITOK);
>> > + =C2=A0 =C2=A0 =C2=A0 cdp =3D malloc(sizeof *cdp, M_CDEVP, M_USE_RESE=
RVE | M_ZERO | M_NOWAIT);
>> >
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0cdp->cdp_dirents =3D &cdp->cdp_dirent0;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0cdp->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)
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return;
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (devsw->d_flags & D_NEEDGIANT) {
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0dev_unlock();
>> > - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 dsw2 =3D malloc(siz=
eof *dsw2, M_DEVT, M_WAITOK);
>> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 dsw2 =3D malloc(siz=
eof *dsw2, M_DEVT, M_NOWAIT);
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0dev_lock();
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0} else
>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0dsw2 =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 conversion.
>> I'm unable to check the code right now.
>
> Sure. Something like this.
>
At this point I wonder what's the purpose of maintaining the sleeping
version for such functions?
Attilio
--=20
Peace can only be achieved by understanding - A. Einstein
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