Re: [PATCH 25/26] r/o bind mounts: scalable writer count

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> This uses a statically-allocated percpu variable.  All
> operations are local to a cpu as long that cpu operates on
> the same mount, and there are no writer count imbalances.
> Writer count imbalances happen when a write is taken on one
> cpu, and released on another, like when an open/close pair
> is performed on two different cpus because the task moved.
> 

I'd suggest something along these lines in final mntput:

	lock_and_coalesce_cpu_mnt_writer_counts();
	mnt_unlock_cpus();
	BUG_ON(atomic_read(&mnt->__mnt_writers));

since there's basically no other we'll notice if there _is_ an
imbalance.

Miklos
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