On Thu, 25 Oct 2012, Peter Zijlstra wrote:
> So I think the below should work, we hold the spinlock over both rb-tree
> modification as sp free, this makes mpol_shared_policy_lookup() which
> returns the policy with an incremented refcount work with just the
> spinlock.
>
> Comments?
>
It's rather unfortunate that we need to protect modification with a
spinlock and a mutex but since sharing was removed in commit 869833f2c5c6
("mempolicy: remove mempolicy sharing") it requires that sp_alloc() is
blockable to do the whole mpol_new() and rebind if necessary, which could
require mm->mmap_sem; it's not as simple as just converting all the
allocations to GFP_ATOMIC.
It looks as though there is no other alternative other than protecting
modification with both the spinlock and mutex, which is a clever
solution, so it looks good to me, thanks!
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