Messages in this thread | | | Date | Thu, 29 Sep 2011 10:06:40 -0700 | From | David Daney <> | Subject | Re: Jump Label initialization |
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On 09/29/2011 09:45 AM, Jeremy Fitzhardinge wrote: > On 09/29/2011 05:04 AM, Jan Glauber wrote: >> >> s390 does not have the early() variant since it didn't need it. On >> pre-SMP we probably don't need stop_machine() so creating >> arch_jump_label_transform_early() by leaving out stop_machine() >> and patching the code directly should be fine. > > Well, it occurs to me that if you're using jump_label_enable() very > early, then it will be using the full arch_jump_label_transform() > anyway. While the stop_machine(), locking, etc that the full version > does is redundant in a pre-SMP environment, it shouldn't hurt, so > perhaps there's no need for an _early variant at all. >
You need a way to guarantee that the code you are modifying is not in the instruction cache of the off-line CPUs.
On our (Cavium) SMP MIPS systems, these off-line CPUs are most likely spinning in architecture specific smp startup code somewhere in the kernel image. If this code happened to be adjacent to something the arch_jump_label_transform_early() would touch, we could have a problem.
The solution is fairly simple, just invalidate the instruction cache immediately upon leaving the spinning loop.
David Daney
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