Re: Regression in 2.6.23-rc2-mm2, mounting cpusets causes a hang

[Lee Schermerhorn]

On Tue, 2007-08-14 at 15:49 -0500, Serge E. Hallyn wrote:
> Quoting Serge E. Hallyn (serge@xxxxxxxxxx):
> > Quoting Lee Schermerhorn (Lee.Schermerhorn@xxxxxx):
> > > On Tue, 2007-08-14 at 13:03 -0500, Serge E. Hallyn wrote:
> > > > Quoting Lee Schermerhorn (Lee.Schermerhorn@xxxxxx):
> > > > > On Mon, 2007-08-13 at 15:12 -0500, Serge E. Hallyn wrote:
> > > > > > Quoting Dhaval Giani (dhaval@xxxxxxxxxxxxxxxxxx):
> > > > > > > Hi,
> > > > > > > 
> > > > > > > On mounting cpusets using containers, I have been hitting the following
> > > > > > > bug.
> > > > > > > 
> > > > > > > 
> > > > > > > -----------[ cut here ]------------
> > > > > > > kernel BUG at kernel/cpuset.c:331!
> > > > > <snip>
> > > > > > > CONFIG_HIGHMEM=y
> > > > > > > CONFIG_X86_PAE=y
> > > > > > > # CONFIG_NUMA is not set
> > > > > > > CONFIG_ARCH_POPULATES_NODE_MAP=y
> > > > > > > CONFIG_SELECT_MEMORY_MODEL=y
> > > > > > > CONFIG_FLATMEM_MANUAL=y
> > > > > > > # CONFIG_DISCONTIGMEM_MANUAL is not set
> > > > > > > # CONFIG_SPARSEMEM_MANUAL is not set
> > > > > > > CONFIG_FLATMEM=y
> > > > > > > CONFIG_FLAT_NODE_MEM_MAP=y
> > > > > > > # CONFIG_SPARSEMEM_STATIC is not set
> > > > > > > CONFIG_SPLIT_PTLOCK_CPUS=4
> > > > > > > CONFIG_RESOURCES_64BIT=y
> > > > > > > CONFIG_ZONE_DMA_FLAG=1
> > > > > <snip>
> > > > > > 
> > > > > > Yeah, I'm seeing the same thing.  Oddly, my node_states[N_NORMAL_MEMORY]
> > > > > > and node_states[N_HIGH_MEMORY] are empty, while node_states[N_ONLINE]
> > > > > > contains my single cpu (on i386 kvm image).
> > > > > > 
> > > > > > -serge
> > > > > 
> > > > > Yes, you'll definitely hit that BUG if the N_HIGH_MEMORY mask is empty.
> > > > > So far, I can't see how this could be, tho'.  __build_all_zonelists()
> > > > > should be called for non-NUMA as well as NUMA.  It iterates over "all
> > > > 
> > > > Yup, and it is, and some debug statements insist that
> > > > node_set_state(nid, N_HIGH_MEMORY) is being called for cpu 0,
> > > > and the state is in fact being correctly set.
> > > > 
> > > > So it must get cleared later...
> > > 
> > > OK.  That helps.  I'll see what I can find...
> > 
> > Well apparently I lied?  I don't think it's getting cleared in node_states.
> > I'm doing:
> > 
> > static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
> > {
> >         int nid=0;
> >         printk(KERN_NOTICE "%s: at top, node %d is %d\n",
> >                 __FUNCTION__, nid, node_state(nid, N_HIGH_MEMORY));
> >         while (cs && !nodes_intersects(cs->mems_allowed,
> >                                         node_states[N_HIGH_MEMORY])) {
> >                 printk(KERN_NOTICE "%s: in loop\n", __FUNCTION__);
> >                 cs = cs->parent;
> >         }
> >         if (cs) {
> >                 printk(KERN_NOTICE "%s: cs was true\n", __FUNCTION__);
> >                 nodes_and(*pmask, cs->mems_allowed,
> >                                         node_states[N_HIGH_MEMORY]);
> >         }
> >         else
> >         {
> >                 printk(KERN_NOTICE "%s: cs was false\n", __FUNCTION__);
> >                 *pmask = node_states[N_HIGH_MEMORY];
> >         }
> >         printk(KERN_NOTICE "%s: at bottom, node %d is %d\n",
> >                 __FUNCTION__, nid, node_state(nid, N_HIGH_MEMORY));
> >         printk(KERN_NOTICE "%s: at bottom, in pmask node %d is %d\n",
> >                 __FUNCTION__, nid, node_isset(nid, *pmask));
> >         BUG_ON(!nodes_intersects(*pmask, node_states[N_HIGH_MEMORY]));
> > }
> > 
> > and getting:
> > 
> > guarantee_online_mems: in loop
> > guarantee_online_mems: cs was false
> > guarantee_online_mems: at bottom, node 0 is 1
> > guarantee_online_mems: at bottom, in pmask node 0 is 0
> > 
> > 
> > So I'm guess that
> > 	*pmask = node_states[N_HIGH_MEMORY];
> > isn't doing what it was intended to do?  That or I've got node_state()
> > wrong...
> 
> Argh.
> 
> CONFIG_NODES_SHIFT was unset, so MAX_NUMNODES=1, so
> node_state() and node_set_state() are dummies.
> 
> So __build_all_zonelists is using the dummy node_state() and
> not actually setting node_states[N_HIGH_MEMORY], and my debug
> statements were using the dumy node_state() which returns 1
> if n==0  :)

Yeah, I saw that, but I was barking up the wrong tree vis a vis the
structure assignment vs memcpy() :-(  Please disregard previous mail.

> 
> Here is a patch which fixes the bug on my system.  As noted in
> the patch description, there are other calls to node_set_state() in
> mm/page_alloc.c which might also need to be switched to node_set(),
> if this is deemed the right solution.

Yeah.  I think that in the node_state initialization functions, we want
to avoid the node_state() wrappers.  They do the right thing for users
of the interfaces, but not for setting up the state masks.

> 
> thanks,
> -serge

Thank you for tracking this down.

Lee


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