On Wed, Dec 02, 2015 at 12:36:54PM +0000, Will Deacon wrote: > On Sat, Nov 28, 2015 at 03:50:09PM +0800, Li Bin wrote: > > On arm64, kstop_machine which is hugely disruptive to a running > > system is not needed to convert nops to ftrace calls or back, > > because that modifed code is a single 32bit instructions which > > is impossible to cross cache (or page) boundaries, and the used str > > instruction is single-copy atomic. > > This commit message is misleading, since the single-copy atomicity > guarantees don't apply to the instruction-side. Instead, the architecture > calls out a handful of safe instructions in "Concurrent modification and > execution of instructions". > > Now, those safe instructions *do* include NOP, B and BL, so that should > be sufficient for ftrace provided that we don't patch condition codes > (and I don't think we do).
Thinking about this some more, you also need to fix the validate=1 case in ftrace_modify_code so that it can run outside of stop_machine. We currently rely on that to deal with concurrent modifications (e.g. module unloading). Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
