Re: More linux-2.6.9 module problems

From: Mike Waychison
Date: Tue Nov 09 2004 - 14:58:12 EST

Hash: SHA1

linux-os wrote:
> I have a memory-test procedure that tests
> memory on a board, accessed via the PCI bus.
> There is a lot of RAM and it's bank-switched
> into some 64k windows so it takes a lot of
> time to test, about 60 seconds.
> This is in a module, therefore inside the kernel.
> When it is invoked via an ioctl() call, the
> kernel is frozen for the whole test-time. The
> test procedure does not use any spin-locks nor
> does it even use any semaphores. It just does a
> bunch of read/write operations over the PCI/Bus.
> I thought that I could enable the preemptible-
> kernel option and the machine would then respond
> normally. Not so. Even with 4 CPUs, when one
> ioctl() is busy in the kernel, nothing else
> happens until its done. Even keyboard activity
> is gone, no Caps Lock and no Num Lock, no `ping`
> response over the network. However, the machine
> comes back to life when the memory-test is done.
> This is kernel version 2.6.9. Is it possible that
> somebody left on the BKL when calling a module
> ioctl() on this version? If not, what do I do
> to be able to execute a time-consuming procedure
> from inside the kernel? Do I break it up into
> sections and execute schedule() periodically
> (temporary work-around --works)??

The BKL has always been grabbed across ioctls. Drop the lock when you
enter your f_op->ioctl call and grab it again open completion.

- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice

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