The patch titled
memcg: fix oops on NULL lru list
has been removed from the -mm tree. Its filename was
memcg-fix-oops-on-null-lru-list.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: memcg: fix oops on NULL lru list
From: Hugh Dickins <hugh@xxxxxxxxxxx>
While testing force_empty, during an exit_mmap, __mem_cgroup_remove_list
called from mem_cgroup_uncharge_page oopsed on a NULL pointer in the lru list.
I couldn't see what racing tasks on other cpus were doing, but surmise that
another must have been in mem_cgroup_charge_common on the same page, between
its unlock_page_cgroup and spin_lock_irqsave near done (thanks to that kzalloc
which I'd almost changed to a kmalloc).
Normally such a race cannot happen, the ref_cnt prevents it, the final
uncharge cannot race with the initial charge. But force_empty buggers the
ref_cnt, that's what it's all about; and thereafter forced pages are
vulnerable to races such as this (just think of a shared page also mapped into
an mm of another mem_cgroup than that just emptied). And remain vulnerable
until they're freed indefinitely later.
This patch just fixes the oops by moving the unlock_page_cgroups down below
adding to and removing from the list (only possible given the previous patch);
and while we're at it, we might as well make it an invariant that
page->page_cgroup is always set while pc is on lru.
But this behaviour of force_empty seems highly unsatisfactory to me: why have
a ref_cnt if we always have to cope with it being violated (as in the earlier
page migration patch). We may prefer force_empty to move pages to an orphan
mem_cgroup (could be the root, but better not), from which other cgroups could
recover them; we might need to reverse the locking again; but no time now for
such concerns.
Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff -puN mm/memcontrol.c~memcg-fix-oops-on-null-lru-list mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-fix-oops-on-null-lru-list
+++ a/mm/memcontrol.c
@@ -623,13 +623,13 @@ retry:
goto retry;
}
page_assign_page_cgroup(page, pc);
- unlock_page_cgroup(page);
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_add_list(pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
+ unlock_page_cgroup(page);
done:
return 0;
out:
@@ -677,14 +677,14 @@ void mem_cgroup_uncharge_page(struct pag
VM_BUG_ON(pc->ref_cnt <= 0);
if (--(pc->ref_cnt) == 0) {
- page_assign_page_cgroup(page, NULL);
- unlock_page_cgroup(page);
-
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_remove_list(pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
+ page_assign_page_cgroup(page, NULL);
+ unlock_page_cgroup(page);
+
mem = pc->mem_cgroup;
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
@@ -736,23 +736,24 @@ void mem_cgroup_page_migration(struct pa
return;
}
- page_assign_page_cgroup(page, NULL);
- unlock_page_cgroup(page);
-
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_remove_list(pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
+ page_assign_page_cgroup(page, NULL);
+ unlock_page_cgroup(page);
+
pc->page = newpage;
lock_page_cgroup(newpage);
page_assign_page_cgroup(newpage, pc);
- unlock_page_cgroup(newpage);
mz = page_cgroup_zoneinfo(pc);
spin_lock_irqsave(&mz->lru_lock, flags);
__mem_cgroup_add_list(pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
+
+ unlock_page_cgroup(newpage);
}
/*
_
Patches currently in -mm which might be from hugh@xxxxxxxxxxx are
git-unionfs.patch
mmap_region-cleanup-the-final-vma_merge-related-code.patch
mm-use-zonelists-instead-of-zones-when-direct-reclaiming-pages.patch
mm-introduce-node_zonelist-for-accessing-the-zonelist-for-a-gfp-mask.patch
mm-remember-what-the-preferred-zone-is-for-zone_statistics.patch
mm-use-two-zonelist-that-are-filtered-by-gfp-mask.patch
mm-have-zonelist-contains-structs-with-both-a-zone-pointer-and-zone_idx.patch
mm-filter-based-on-a-nodemask-as-well-as-a-gfp_mask.patch
mm-try-both-endianess-when-checking-for-endianess.patch
procfs-task-exe-symlink.patch
procfs-task-exe-symlink-fix.patch
procfs-task-exe-symlink-fix-2.patch
prio_tree-debugging-patch.patch
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