On 06/01/2011 02:39 PM, Michal Hocko wrote:
On Wed 01-06-11 12:44:04, Igor Mammedov wrote:
Freshly allocated 'mem_cgroup_per_node' list entries must be
initialized before the rest of the kernel can see them. Otherwise
zero initialized list fields can lead to race condition at
mem_cgroup_force_empty_list:
pc = list_entry(list->prev, struct page_cgroup, lru);
where 'pc' will be something like 0xfffffffc if list->prev is 0
and cause page fault later when 'pc' is dereferenced.
Have you ever seen such a race? I do not see how this could happen.
mem_cgroup_force_empty_list is called only from
mem_cgroup_force_empty_write (aka echo whatever> group/force_empty)
or mem_cgroup_pre_destroy when the group is destroyed.
The initialization code is, however, called before a group is
given for use AFICS.
I am not saying tha the change is bad, I like it, but I do not think it
is a fix for potential race condition.
Yes I've seen it (RHBZ#700565). It causes random crashes
in virt env ocasionally. It's easier to reproduce if you overcommit
cpu.
Signed-off-by: Igor Mammedov<imammedo@xxxxxxxxxx>
---
mm/memcontrol.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bd9052a..ee7cb4c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4707,7 +4707,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
if (!pn)
return 1;
- mem->info.nodeinfo[node] = pn;
for (zone = 0; zone< MAX_NR_ZONES; zone++) {
mz =&pn->zoneinfo[zone];
for_each_lru(l)
@@ -4716,6 +4715,7 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
mz->on_tree = false;
mz->mem = mem;
}
+ mem->info.nodeinfo[node] = pn;
return 0;
}
--
1.7.1
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