Messages in this thread | | | Date | Tue, 4 Aug 2020 19:01:53 +0200 | From | peterz@infradea ... | Subject | Re: [RFC PATCH 2/2] sched: membarrier: cover kthread_use_mm |
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On Tue, Aug 04, 2020 at 10:59:33AM -0400, Mathieu Desnoyers wrote: > ----- On Aug 4, 2020, at 10:51 AM, Peter Zijlstra peterz@infradead.org wrote: > > On Tue, Jul 28, 2020 at 12:00:10PM -0400, Mathieu Desnoyers wrote:
> >> task_lock(tsk); > >> + /* > >> + * When a kthread stops operating on an address space, the loop > >> + * in membarrier_{private,global}_expedited() may not observe > >> + * that tsk->mm, and not issue an IPI. Membarrier requires a > >> + * memory barrier after accessing user-space memory, before > >> + * clearing tsk->mm. > >> + */ > >> + smp_mb(); > >> sync_mm_rss(mm); > >> local_irq_disable(); > > > > Would it make sense to put the smp_mb() inside the IRQ disable region? > > I've initially placed it right after task_lock so we could eventually > have a smp_mb__after_non_raw_spinlock or something with a much better naming, > which would allow removing the extra barrier when it is implied by the > spinlock.
Oh, right, fair enough. I'll go think about if smp_mb__after_spinlock() will work for mutexes too.
It basically needs to upgrade atomic*_acquire() to smp_mb(). So that's all architectures that have their own _acquire() and an actual smp_mb__after_atomic().
Which, from the top of my head are only arm64, power and possibly riscv. And if I then git-grep smp_mb__after_spinlock, all those seem to be covered.
But let me do a better audit..
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