Re: More linux-2.6.9 module problems

From: linux-os
Date: Tue Nov 09 2004 - 15:27:09 EST


On Tue, 9 Nov 2004, Mike Waychison wrote:

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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.


Hmmm. I get 'scheduling while atomic' screaming across the screen!
There are no atomic operations in my ioctl functions so I don't
know what its complaining about. I think I shouldn't have tried
to do anything with BKL because I (my task) doesn't own it.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.9 on an i686 machine (5537.79 BogoMips).
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