Re: [patch] cpusets: do not allow TIF_MEMDIE tasks to allocate globally

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2007-06-06 at 00:48 -0700, David Rientjes wrote:
> On Wed, 6 Jun 2007, Paul Jackson wrote:
> 
> > Seems like that mlock code is able then to get great globs of memory
> > without returning to user space ... perhaps that's where the fix
> > should be ... that code should quit chewing up memory if it's
> > marked MEMDIE or some such?
> > 
> 
> That's one case.  Are there others?
> 
> The TIF_MEMDIE exception in cpuset_zone_allowed_softwall() allowed this 
> problem in mlock().  If it had not been allowed to allocate anywhere 
> based simply on the zonelist ordering, the mlock iteration would break 
> because it could not handle the fault.
> 
> Thus, at the least, we should make sure that memory is not allocated 
> outside of a task's mems_allowed unless we do sanity checks against 
> gfp_mask in the TIF_MEMDIE case via cpuset_zone_allowed_softwall() to make 
> sure a rouge application doesn't cause the same trouble.  That is, unless 
> you can guarantee this type of problem will not happen again through any 
> other means.  The logic needs to be with the TIF_MEMDIE exception to grant 
> access to memory outside the cpuset only when it is relevant to the OOM 
> killed task's prompt exit.

I don't think your patch alone would have been sufficient. With it it
would have depleted the local reserves and then jumped onwards to other
nodes (since the ALLOC_NO_WATERMARKS allocation doesn't have
ALLOC_CPUSET).

Unless there was a mem-policy restricting the zonelist (not sure if
cpusets and mem-policies are independent like that)

But your point stands.