I am trying to track down a forcedeth driver issue described by bug 9047 in bugzilla (2.6.23-rc7-git1 forcedeth w/ MCP55 oops under heavy load). I added a patch to synchronize the timer handlers so that one handler doesn't accidently enable the IRQ while another timer handler is running (see attachment 'Add timer lock' in bug report) and for other processing protection.Either disable_irq() is not working properly or interrupts are nested, i.e. the irq handler is called again while running.
However, the system still had an Oops. So I added a lock around the nv_rx_process_optimized() and the Oops has not happened (see attachment 'New patch for locking' in bug report). This would imply a synchronization issue. However, the only callers of that function are the IRQ handler and the timer handlers (in non-NAPI case). The timer handlers use disable_irq so that the IRQ handler does not contend with them. It looks as if disable_irq is not working properly.