[PATCH] cpqarray SMP deadlock fix
This fixes some critical bugs in cpqarray in 2.5. One of the fixes essentially backs out the block queue stop/start behavior that was added recently. This code as it stands is buggy and locks up under even light SMP workloads. Certainly we want the performance benefits of proper block queue plugging, but the driver needs some work before it will fit nicely. Some of these fixes do theoretically hurt performance, but when you consider that the driver is unusable under SMP as-is, I think it is right to get correctness first. Specifically, this patch does the following: * Adds locking to proc queue-walking code for debugging use. Note that the proc registration is still broken and I've left it that way since this stuff should probably migrate to driverfs anyway. * Moves interrupt enabling so queue lock is initialized before interrupts are enabled. Otherwise if we get a quick interrupt we oops the machine. * Removes unconditional IRQ enabling in do_ida_request(). The block layer takes the spinlock with irq_save so if we're going to play this trick then we need to irq_restore. For now, just eliminate the unlocked region. * Remove block queue stop/start logic since it can leave the queue stopped with no outstanding completions to start it again. Plugging logic can come back but it should go hand-in-hand with a cleanup of the driver's request handling algorithm. If nobody screams about this patch I'll go ahead and start making those improvments.
Showing
Please register or sign in to comment