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-rw-r--r--fs/exec.c2
-rw-r--r--kernel/cgroup.c5
-rw-r--r--kernel/exit.c12
-rw-r--r--mm/memcontrol.c17
4 files changed, 31 insertions, 5 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 32993beecbe9..cecee501ce78 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -752,11 +752,11 @@ static int exec_mmap(struct mm_struct *mm)
tsk->active_mm = mm;
activate_mm(active_mm, mm);
task_unlock(tsk);
- mm_update_next_owner(old_mm);
arch_pick_mmap_layout(mm);
if (old_mm) {
up_read(&old_mm->mmap_sem);
BUG_ON(active_mm != old_mm);
+ mm_update_next_owner(old_mm);
mmput(old_mm);
return 0;
}
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 13932abde159..a0123d75ec9a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2738,14 +2738,15 @@ void cgroup_fork_callbacks(struct task_struct *child)
*/
void cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
{
- struct cgroup *oldcgrp, *newcgrp;
+ struct cgroup *oldcgrp, *newcgrp = NULL;
if (need_mm_owner_callback) {
int i;
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
oldcgrp = task_cgroup(old, ss->subsys_id);
- newcgrp = task_cgroup(new, ss->subsys_id);
+ if (new)
+ newcgrp = task_cgroup(new, ss->subsys_id);
if (oldcgrp == newcgrp)
continue;
if (ss->mm_owner_changed)
diff --git a/kernel/exit.c b/kernel/exit.c
index 16395644a98f..85a83c831856 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -583,8 +583,6 @@ mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
* If there are other users of the mm and the owner (us) is exiting
* we need to find a new owner to take on the responsibility.
*/
- if (!mm)
- return 0;
if (atomic_read(&mm->mm_users) <= 1)
return 0;
if (mm->owner != p)
@@ -627,6 +625,16 @@ retry:
} while_each_thread(g, c);
read_unlock(&tasklist_lock);
+ /*
+ * We found no owner yet mm_users > 1: this implies that we are
+ * most likely racing with swapoff (try_to_unuse()) or /proc or
+ * ptrace or page migration (get_task_mm()). Mark owner as NULL,
+ * so that subsystems can understand the callback and take action.
+ */
+ down_write(&mm->mmap_sem);
+ cgroup_mm_owner_callbacks(mm->owner, NULL);
+ mm->owner = NULL;
+ up_write(&mm->mmap_sem);
return;
assign_new_owner:
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c0500e4d3a2f..36896f3eb7f5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -250,6 +250,14 @@ static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
+ /*
+ * mm_update_next_owner() may clear mm->owner to NULL
+ * if it races with swapoff, page migration, etc.
+ * So this can be called with p == NULL.
+ */
+ if (unlikely(!p))
+ return NULL;
+
return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
struct mem_cgroup, css);
}
@@ -549,6 +557,11 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
if (likely(!memcg)) {
rcu_read_lock();
mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
+ if (unlikely(!mem)) {
+ rcu_read_unlock();
+ kmem_cache_free(page_cgroup_cache, pc);
+ return 0;
+ }
/*
* For every charge from the cgroup, increment reference count
*/
@@ -801,6 +814,10 @@ int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
rcu_read_lock();
mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
+ if (unlikely(!mem)) {
+ rcu_read_unlock();
+ return 0;
+ }
css_get(&mem->css);
rcu_read_unlock();