Helge Deller 706ad8dcb5 parisc: Filter out spurious interrupts in PA-RISC irq handler ... commit b1b4e435e4ef7de77f07bf2a42c8380b960c2d44 upstream. When detecting a serial port on newer PA-RISC machines (with iosapic) we have a long way to go to find the right IRQ line, registering it, then registering the serial port and the irq handler for the serial port. During this phase spurious interrupts for the serial port may happen which then crashes the kernel because the action handler might not have been set up yet. So, basically it's a race condition between the serial port hardware and the CPU which sets up the necessary fields in the irq sructs. The main reason for this race is, that we unmask the serial port irqs too early without having set up everything properly before (which isn't easily possible because we need the IRQ number to register the serial ports). This patch is a work-around for this problem. It adds checks to the CPU irq handler to verify if the IRQ action field has been initialized already. If not, we just skip this interrupt (which isn't critical for a serial port at bootup). The real fix would probably involve rewriting all PA-RISC specific IRQ code (for CPU, IOSAPIC, GSC and EISA) to use IRQ domains with proper parenting of the irq chips and proper irq enabling along this line. This bug has been in the PA-RISC port since the beginning, but the crashes happened very rarely with currently used hardware. But on the latest machine which I bought (a C8000 workstation), which uses the fastest CPUs (4 x PA8900, 1GHz) and which has the largest possible L1 cache size (64MB each), the kernel crashed at every boot because of this race. So, without this patch the machine would currently be unuseable. For the record, here is the flow logic: 1. serial_init_chip() in 8250_gsc.c calls iosapic_serial_irq(). 2. iosapic_serial_irq() calls txn_alloc_irq() to find the irq. 3. iosapic_serial_irq() calls cpu_claim_irq() to register the CPU irq 4. cpu_claim_irq() unmasks the CPU irq (which it shouldn't!) 5. serial_init_chip() then registers the 8250 port. Problems: - In step 4 the CPU irq shouldn't have been registered yet, but after step 5 - If serial irq happens between 4 and 5 have finished, the kernel will crash Signed-off-by: Helge Deller <deller@gmx.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2015-10-01 12:07:32 +02:00
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kernel	parisc: Filter out spurious interrupts in PA-RISC irq handler	2015-10-01 12:07:32 +02:00
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