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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.