Messages in this thread | | | Date | Tue, 26 Nov 2019 09:11:04 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH -v5 00/17] Rewrite x86/ftrace to use text_poke (and more) |
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On Mon, 25 Nov 2019 12:32:45 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 25 Nov 2019 12:55:34 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries) > > ... > > on_each_cpu(do_sync_core, NULL, 1); > > /* > > * sync_core() implies an smp_mb() and orders this store against > > * the writing of the new instruction. > > */ > > bp_patching.vec = NULL; > > bp_patching.nr_entries = 0; > > } > > ----- > > > > I think the "on_each_cpu(do_sync_core, NULL, 1);" can sync the pipeline > > but doesn't ensure all ongoing int3 handling is done. Thus, we may need a > > How does it not ensure all ongoing int3 handling is done? int3 is done > with interrupts disabled, and the on_each_cpu() requires all CPUs to > have had their interrupts enabled, thus int3 handling should be > completed. Perhaps we need another sync core? > > on_each_cpu(do_sync_core, NULL, 1); > bp_patching.nr_entries = 0; > on_each_cpu(do_sync_core, NULL, 1); > bp_patching.vec = NULL;
OK, let me check.
The 1st sync_core will ensure the poking "int3" is removed. Thus any int3-hit address (ip) should NOT match the bp_patching.vec[*].addr after that. At this point, "if (likely(!bp_patching.nr_entries))" check does not work.
And the 2nd sync_core will ensure all poke_int3_handler() will see the bp_patching.nr_entries = 0. After this point, "if (likely(!bp_patching.nr_entries))" works and poke_int3_handler() will exit soon. (before touching bp_patching.vec)
So this looks good to me.
Thank you!
-- Masami Hiramatsu <mhiramat@kernel.org>
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