From: Lee Revell <rlrevell@joe-job.com>
To: "Michael S. Tsirkin" <mst@mellanox.co.il>
Cc: linux-kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: f_ops flag to speed up compatible ioctls in linux kernel
Date: Wed, 01 Sep 2004 17:38:29 -0400 [thread overview]
Message-ID: <1094074708.1343.19.camel@krustophenia.net> (raw)
In-Reply-To: <20040901212314.GA26044@mellanox.co.il>
On Wed, 2004-09-01 at 17:23, Michael S. Tsirkin wrote:
> Hello!
> Quoting r. Albert Cahalan (albert@users.sourceforge.net) "Re: f_ops flag to speed up compatible ioctls in linux kernel":
> > Michael S. Tsirkin writes:
> > > Quoting Lee Revell [snip -- that was excessive]
> >
> > >> By adding a new ioctl you are adding a new use of
> > >> the BKL. It has been suggested on dri-devel that
> > >> this should be fixed. Is this even possible?
> > >
> > > I dont know - can the lock be released before the
> > > call to filp->f_op->ioctl ?
> > >
> > > I assume the reason its there is for legacy
> > > code - existing ioctls may be assuming the BKL
> > > is taken, but maybe there could be another flag
> > > in f_ops to let sys_ioctl release the lock before
> > > doing the call ...
> > >
> > > Like this - would that be safe?
> >
> > Yes. It is proven to work.
>
> Now that I look at the ioctl.c code, I see a several get_user/put_user
> inside the ioctl which are thus done while BKL is held.
> But I thought get_user can block?
>
> Why is this not a bug?
>
You can sleep while holding the BKL, it is automatically dropped and
reacquired. The BKL has some magic properties, it does not work like a
regular spinlock.
Lee
next prev parent reply other threads:[~2004-09-01 21:46 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-01 15:40 f_ops flag to speed up compatible ioctls in linux kernel Albert Cahalan
2004-09-01 21:23 ` Michael S. Tsirkin
2004-09-01 21:38 ` Lee Revell [this message]
2004-09-01 21:43 ` Chris Wright
2004-09-01 21:44 ` Roland Dreier
-- strict thread matches above, loose matches on Subject: below --
2004-12-27 22:22 Michael S. Tsirkin
2004-09-01 15:36 Albert Cahalan
2004-09-01 15:59 ` Roland Dreier
2004-09-01 21:53 ` Michael S. Tsirkin
2004-09-01 22:58 ` Roland Dreier
2004-09-01 23:18 ` Michael S. Tsirkin
2004-09-01 9:50 filia
2004-09-01 9:52 ` Arjan van de Ven
2004-09-01 10:16 ` filia
[not found] ` <4135B9FC.7050602@hist.no>
2004-09-01 13:29 ` Ihar 'Philips' Filipau
2004-09-01 15:28 ` Ihar 'Philips' Filipau
2004-09-02 7:29 ` Helge Hafting
2004-09-01 13:43 ` Olivier Galibert
2004-09-01 7:22 Michael S. Tsirkin
2004-09-01 7:32 ` viro
2004-09-01 7:44 ` Michael S. Tsirkin
2004-09-01 7:47 ` Lee Revell
2004-09-01 8:19 ` Michael S. Tsirkin
2004-09-01 15:55 ` Roland Dreier
2004-09-01 18:02 ` Chris Wright
2004-09-01 18:12 ` Roland Dreier
2004-09-01 18:31 ` viro
2004-09-01 20:54 ` Roland Dreier
[not found] ` <20040901170800.K1924@build.pdx.osdl.net>
[not found] ` <20040901190122.L1924@build.pdx.osdl.net>
2004-09-02 3:46 ` Roland Dreier
2004-09-01 18:06 ` Bill Davidsen
2004-09-01 8:30 ` Arjan van de Ven
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