On Tue, Feb 21, 2017 at 03:10:45PM +0900, Ho-Eun Ryu wrote: > > On 20 Feb 2017, at 7:02 PM, Mark Rutland <[email protected]> wrote: > > On Sun, Feb 19, 2017 at 07:03:38PM +0900, Hoeun Ryu wrote: > >> After `__ro_after_init` marker is included in kernel, many kernel data > >> objects can be read-only-after-init. But there are many other places that > >> would be good to read-only-after-init but `__ro_after_init` can not be > >> simply > >> applicable to them because they should be writable at some points, which > >> are > >> during module_init/exit or dynamic de/registration for a specific > >> subsystem. > > > > Could you elaborate on this? > > > > For modules, I assume that the __ro_after_init data structures are part > > of the module, and not part of the "real" kernel image. Is that the case? > > __ro_mostly_after_init is for kernel builtin core subsystems, not for > modules themselves. The section can be writable only during kernel > init and module_init/exit. Some hooks (or array of hooks) of a core > subsystem can be marked as __ro_mostly_after_init similar to that way > of __ro_after_init. After that some modules that may write to those > hooks of the subsystem to register/deregister something to the > subsystem can safely access those section. Please see RFC 3/7 that > makes this section writable. > > In addition, some subsystems may use this marker for their (array of) > hooks and make them writable only at some point of time via > set_ro_mostly_after_init_rw/ro pair. please read RFC 4/7 for selinux.
Ok. This sounds like a limited case of __write_rarely, where we only expect to perform writes in specific time windows. I'd prefer if we could attack __write_rarely, and use the appraoch to cater for this case, but I am not necessarily opposed to this approach if other architectures are happy with it. > > Which specific subsystems whish to modify data structures that are > > __ro_after_init? > > I’m not intending to make writable __ro_after_init section but > introducing new section marker that works mostly like __ro_after_init > but can be written to at some points. please see RFC 5/7 for > cpuhotplug. Ah. I clearly had not read this sufficiently thoroughly; sorry about that. Thanks, Mark.
