Re: [patch for-3.7] mm, mempolicy: fix printing stack contents innuma_maps

[David Rientjes]

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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