Hi, trying to port the generic device interrupt masking pattern of uio_pci_generic to KVM's device assignment code, I stumbled over some fundamental problem with the current pci_block/unblock_user_cfg_access interface: it does not provide any synchronization between blocking sides. This allows user space to trigger a kernel BUG, just run two while true; do echo 1 > /sys/bus/pci/devices/<some-device>/reset; done loops in parallel and watch the kernel oops. Instead of some funky open-coded locking mechanism, we would rather need a plain mutex across both the user space access (via sysfs) and the sections guarded by pci_block/unblock_user_cfg_access so far. But I'm not sure which of them already allow sleeping, specifically if the IPR driver would be fine with such a change. Can someone in the CC list comment on this? uio_pci_generic would definitely not be able to sleep as it takes the lock from (potentially hard) IRQ context. This particular use case, RMW of command/status word, requires a separate mechanism. I'm considering to introduce a dedicated raw spinlock with IRQ protection for that words, maybe also a PCI core service to abstract INTx testing and masking. Any further thoughts on how to resolve this issue? Thanks, Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
