Messages in this thread | | | Subject | Re: [PATCH 10/10] mm,sched: conditionally skip lazy TLB mm refcounting | From | Rik van Riel <> | Date | Sun, 29 Jul 2018 08:11:59 -0400 |
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On Sat, 2018-07-28 at 21:21 -0700, Andy Lutomirski wrote: > On Sat, Jul 28, 2018 at 2:53 PM, Rik van Riel <riel@surriel.com> > wrote: > > Conditionally skip lazy TLB mm refcounting. When an architecture > > has > > CONFIG_ARCH_NO_ACTIVE_MM_REFCOUNTING enabled, an mm that is used in > > lazy TLB mode anywhere will get shot down from exit_mmap, and there > > in no need to incur the cache line bouncing overhead of refcounting > > a lazy TLB mm. > > Unless I've misunderstood something, this patch results in idle tasks > whose active_mm has been freed still having active_mm pointing at > freed memory.
Patch 9/10 is supposed to ensure that the lazy TLB CPUs get switched to init_mm before an mm is freed. No CPU should ever have its active_mm pointing at a freed mm.
Your message made me re-read the code, and now I realize that leave_mm does not actually do that.
Looking at the other callers of leave_mm, I might not be the only one surprised by that; xen_drop_mm_ref comes to mind.
I guess I should some code to leave_mm to have it actually clear active_mm and call the conditional refcount drop helper function.
Does that clear up the confusion?
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