Messages in this thread | | | Date | Wed, 2 Jan 2013 10:30:53 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH 1/2] tmpfs mempolicy: fix /proc/mounts corrupting memory |
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On Wed, 2 Jan 2013, Christoph Lameter wrote: > On Wed, 2 Jan 2013, Hugh Dickins wrote: > > > Recent NUMA enhancements are not to blame: this dates back to 2.6.35, > > when commit e17f74af351c "mempolicy: don't call mpol_set_nodemask() > > when no_context" skipped mpol_parse_str()'s call to mpol_set_nodemask(), > > which used to initialize v.preferred_node, or set MPOL_F_LOCAL in flags. > > With slab poisoning, you can then rely on mpol_to_str() to set the bit > > for node 0x6b6b, probably in the next page above the caller's stack. > > Ugly. But 2.6.35 means that the patch was not included in several > enterprise linux releases.
Thanks, that's some relief. I forgot to mention that a good test for whether your particular kernel (with who knows what additional patches applied) is affected, is to
mount -o remount,mpol=local /dev/shm # which should be a tmpfs grep /dev/shm /proc/mounts
If that says "mpol=prefer" then you're affected and need the fix; if it says "mpol=local" (like 2.6.34 or after this fix) then you're safe.
(Conversely, setting "mpol=prefer" shows up as "mpol=local" after the, fix, since that's what prefer without a node specification amounts to.)
> > > I don't understand why MPOL_LOCAL is described as a pseudo-policy: > > it's a reasonable policy which suffers from a confusing implementation > > in terms of MPOL_PREFERRED with MPOL_F_LOCAL. I believe this would be > > much more robust if MPOL_LOCAL were recognized in switch statements > > throughout, MPOL_F_LOCAL deleted, and MPOL_PREFERRED use the (possibly > > empty) nodes mask like everyone else, instead of its preferred_node > > variant (I presume an optimization from the days before MPOL_LOCAL). > > But that would take me too long to get right and fully tested. > > The current approaches to implementing NUMA scheduling are making > MPOL_LOCAL an explicit policy. See > https://patchwork.kernel.org/patch/1703641/.
It's a good step in the right direction.
> > Does that address the concerns?
It makes no difference to this bug, and does not go far enough to remove all the MPOL_F_LOCAL MPOL_PREFERRED MPOL_LOCAL twistiness.
Hugh
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