Hello, I have the following problem: Driver A has a custom mmap() implementation and assigns own vm_ops to a created vma. The process which called mmap() passes the resulting userspace address to another driver, driver B. Driver B would then like to increment usage count on that memory for a duration of some operation, i.e. call vm_ops->open(). It can find_vma() for the userspace address it was given and call vm_ops->open() on found vma. It can then call vm_ops->close() when finished. The problem here though is that the found vm_area_struct (and the userspace address for that matter) might not be valid anymore by the time driver B wants to call close(). There can be three possibilities here: a) vm_area_struct used for open() is still present and can be reused for close() - that looks ok, but storing a pointer to that vma is risky, driver B has no way to know whether the pointer is still valid. b) some other vm_area_structs are still present, but driver B has no knowledge about them - so it does not have anything to pass to close(). c) no vm_area_structs remain, but since we called open() before, driver A is still waiting for driver B to call close(); driver B does not have anything to pass to close() and there is nothing in the system that could be passed to it anyway. I don't suppose copying aside the whoe vm_area_struct used for open() call and passing it back to close() is a good idea. Is there any way to do this? Or maybe I have it all wrong? Thank you, Zenek -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>