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Re: [PLUG] Weird Hang on Boot
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Ok, now for the stupid question: Are there any modules that don't work
with the preemptable patch and/or an SMP kernel? I'm asking because I have
never compiled the 2.4.18 kernel without the patch in place or SMP
disabled on the machine that is giving me problems.
On the 24th day of March in the year 2002 you wrote:
> Date: Sun, 24 Mar 2002 16:13:37 -0500
> From: Will Dyson <will_dyson@pobox.com>
> To: plug@lists.phillylinux.org
> Subject: Re: [PLUG] Weird Hang on Boot
>
> Martin DiViaio wrote:
>
> > I know I've miscompiled the kernel I'm just not sure where. I did run
> > across an article in the SMP-HOWTO that says that odd hangs can occur with
> > some protocol issues. I have compiled SMP support into the kernel but I am
> > not using multiple processors at the moment. Could that be the problem? If
> > not, could it be the preemptable patch? Or both?
>
> An SMP kernel will work fine on a single cpu computer. A non-smp kernel
> will run slightly faster, because it can leave out a lot of the locking
> that a SMP kernel does.
>
> I am running a kernel (2.4.18-pre9) with the preemptable patch, and have
> found it to be quite stable.
>
> However, your problems sound like the kind of thing that would happen if a
> module that was compiled without preemption was loaded into a preemptable
> kernel (or a module compiled without smp support loaded into an smp
> kernel, for that matter).
>
> The preemptable kernel patch modifies the kernel locking mechanisms so
> that preemption is prevented when a lock is held. However, those locking
> mechanisms are compiled inline for speed. Therefor, a module binary that
> was compiled for a non-preemptive kernel will still use the
> non-preempt-aware locking when loaded into a preemptive kernel. This will
> cause all sorts of trouble. For example, imagine that the
> non-preempt-aware module grabs a kernel lock and is then preempted by
> another process which also needs access to the same lock. Deadlock. The
> preempted process cannot give up the lock because it is not running. The
> preempting proccess will wait forever for the lock.
>
> Anyway, to make sure this is not happening, you should boot using a stable
> kernel and rename away (or delete) the modules directory for the 2.4.18
> kernel (/lib/modules/2.4.18/), and then recompile the preemptive kernel.
>
>
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