Re: [PATCH 1/5] Add a map to to track dirty pages per node

[Christoph Lameter <clameter@sgi.com>]

On Fri, 19 Jan 2007, Paul Jackson wrote:

> Christoph wrote:
> > + * Called without the tree_lock! So we may on rare occasions (when we race with
> > + * cpuset_clear_dirty_nodes()) follow the dirty_node pointer to random data.
> 
> Random is ok, on rate occassion, as you note.
> 
> But is there any chance you could follow it to a non-existent memory location
> and oops?  These long nodemasks are kmalloc/kfree'd, and I thought that once
> kfree'd, there was no guarantee that the stale address would even point to
> a mapped page of RAM.  This situation reminds me of the one that led to adding
> some RCU dependent code to kernel/cpuset.c.

This could become an issue if we implement memory unplug and then RCU 
locking could help. But right now that situation is only possible with 
memory mapped via page tables (vmalloc or user space pages). The slab 
allocator can currently only allocate from 1-1 mapped memory. So no danger 
there.



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