On Fri, 24 Jan 2014 17:43:35 +0800, parmenides said:
CONFIG_BROKEN_ON_SMP: should be set in the kernel configuration, but isn't.
I wonder what the meaning of the configuration is. How does it work? Thx!
Drivers (and all other kernel-mode code, actually) need to do proper locking, so that if there's a race between code running on 2 different CPUs at the same time, they don't stomp all over each other (consider the case of one CPU trying to walk a linked list at the same time that another CPU is deleting an entry from the list - this can leave the first CPU walking down a now corrupted list following now-stale pointers). There are a lot of old buggy drivers that don't do proper locking. In a few cases, the drivers are *technically* buggy, but the bugs just happen to be in code that will manage to work anyhow *if there is only one CPU* (for instance, wrapped in a IRQ-disabled section). These drivers get BROKEN_ON_SMP attached, because they can still potentially be useful for people compiling on architectures that only support 1 processor core, or *need* the driver and don't care if they only use 1 core of the 4 they have. The proper fix is, of course, to put proper locking in the driver - but most BROKEN_ON_SMP drivers are creeping horrorshows straight out of HP Lovecraft, and nobody wants to invest the resources needed to fix the abandonware driver.