"upping" a semaphore from interrupt context?

Hello,

I am writing a USB driver for some custom hardware, and I need to
synchronize between the user-space and the USB subsystem.  Can I
create a semaphore and "down" it in the reader then "up" it in the
completion handler?

I know the completion handler runs in interrupt context so you are not
allowed to acquire any semaphores: but can you release them?  Will the
waiting tasks wake up after the handler and its caller returned - IOW
will the waking up task run in interrupt context as well?

This is with Linux 2.4 (if it makes a difference).

Thanks,
florin

-- 
Bruce Schneier expects the Spanish Inquisition.
      http://geekz.co.uk/schneierfacts/fact/163

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