Date: Thu, 21 May 2009 19:05:17 +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: <3bbf2fe10905211005m350dc4d1yed6dc1b79f1603d9@mail.gmail.com> In-Reply-To: <20090521163846.GT1927@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>
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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(). =C2=A0I'd rather not hav=
e to
>> roll my own decoupled version. =C2=A0And I understand the argument about
>> destroy_dev being a drain point for the API. =C2=A0However, what about
>> 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_RESERVE=
| M_ZERO | M_WAITOK);
> + =C2=A0 =C2=A0 =C2=A0 cdp =3D malloc(sizeof *cdp, M_CDEVP, M_USE_RESERVE=
| 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(sizeof=
*dsw2, M_DEVT, M_WAITOK);
> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 dsw2 =3D malloc(sizeof=
*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.
Thanks,
Attilio
--=20
Peace can only be achieved by understanding - A. Einstein
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