From: Gerd Knorr <kraxel@bytesex.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Gerd Knorr <kraxel@suse.de>, Takashi Iwai <tiwai@suse.de>,
"Alexander E. Patrakov" <patrakov@ums.usu.ru>,
lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: modprobe + request_module() deadlock
Date: Mon, 22 Nov 2004 11:25:02 +0100 [thread overview]
Message-ID: <20041122102502.GF29305@bytesex> (raw)
In-Reply-To: <1101026370.18919.32.camel@localhost.localdomain>
> > > MODULE_DEPENDS_ON("somemodule");
> >
> > On the other hand I don't depend on request_module() waiting for the
> > modprobe being finished. So maybe we can solve that with a
> > request_module_async()?
>
> The problem is fairly simple: we don't let you get at the symbols from a
> module which hasn't finished initializing yet. This means that a
> request_module() inside a module's init() will fail if the requested
> module depends on this one. async() will race with init() finishing, so
> won't really help.
Hmm, so module loading is not serialized by a lock? I assumed that
caused the deadlock in $subject which started this thread ...
> The traditional way to do this has been to have saa7134-empress do its
> own probe, and likewise saa7134-dvb.
They can't actually probe themself. It's _one_ PCI device (driven by
the saa7134 module) which can handle (among other v4l-related things)
the DMA transfer of mpeg streams. That can be used in different ways
(or not at all) and the different use cases are handled by the
sub-modules.
So the way it is intended to work is that saa7134 has the pci table and
gets autoloaded by hotplug, it will have a look at the hardware and then
load either saa7134-empress or saa7134-dvb or none of them, so you'll
get everything nicely autoloaded.
> Unfortunately, these days modules are not supposed to fail to load
> simply because there are no devices, so wild module loading has a real
> cost.
Yes, thats exactly the problem. And this is especially true for the
saa7134-dvb module as this one has a bunch of dependencies to other
modules of the dvb subsystem. Thats why I try to avoid loading them
if they are not needed.
> Otherwise I'd be tempted to make multiple aliases load *all* of them,
> and solve the problem that way.
Well, that will actually work. You can simply load both saa7134-empress
and saa7134-dvb, the saa7134 core module will take care that they can
only attach to devices they can actually handle. Drawback is the memory
footprint ...
Gerd
--
#define printk(args...) fprintf(stderr, ## args)
next prev parent reply other threads:[~2004-11-22 10:43 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-17 22:29 modprobe + request_module() deadlock Johannes Stezenbach
2004-11-18 3:48 ` Rusty Russell
2004-11-18 13:55 ` Johannes Stezenbach
2004-11-18 19:05 ` Takashi Iwai
2004-11-19 4:04 ` Alexander E. Patrakov
2004-11-19 11:10 ` Takashi Iwai
2004-11-19 11:50 ` Gerd Knorr
2004-11-19 12:42 ` Alexander E. Patrakov
2004-11-21 8:39 ` Rusty Russell
2004-11-22 10:25 ` Gerd Knorr [this message]
2004-11-22 14:16 ` Johannes Stezenbach
2004-11-22 14:44 ` Gerd Knorr
2004-11-22 15:36 ` Johannes Stezenbach
2004-11-22 16:52 ` Gerd Knorr
2004-11-24 5:02 ` Rusty Russell
2004-11-24 12:11 ` Gerd Knorr
2004-11-25 16:03 ` Gerd Knorr
2004-11-26 0:34 ` Rusty Russell
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