On Thu, 2020-12-03 at 12:31 +0000, Matthew Wilcox wrote: > And this just makes me think RCU freeing of mm_struct. I'm sure it's > more complicated than that (then, or now), but if an anonymous > process > is borrowing a freed mm, and the mm is freed by RCU then it will not > go > away until the task context switches. When we context switch back to > the anon task, it'll borrow some other task's MM and won't even > notice > that the MM it was using has gone away. One major complication here is that most of the active_mm borrowing is done by the idle task, but RCU does not wait for idle tasks to context switch. That means RCU, as it is today, is not a mechanism that mm_struct freeing could just piggyback off. -- All Rights Reversed.
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