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authorDaisuke Nishimura2011-01-13 15:47:41 -0800
committerLinus Torvalds2011-01-13 17:32:51 -0800
commitdfe076b0971a783469bc2066e85d46e23c8acb1c (patch)
treeee0856c119ed898212da2555f936fb3284c5ff59
parent043d18b1e5bdfc4870b8a19d00f0d5c636a5c231 (diff)
memcg: fix deadlock between cpuset and memcg
Commit b1dd693e ("memcg: avoid deadlock between move charge and try_charge()") can cause another deadlock about mmap_sem on task migration if cpuset and memcg are mounted onto the same mount point. After the commit, cgroup_attach_task() has sequence like: cgroup_attach_task() ss->can_attach() cpuset_can_attach() mem_cgroup_can_attach() down_read(&mmap_sem) (1) ss->attach() cpuset_attach() mpol_rebind_mm() down_write(&mmap_sem) (2) up_write(&mmap_sem) cpuset_migrate_mm() do_migrate_pages() down_read(&mmap_sem) up_read(&mmap_sem) mem_cgroup_move_task() mem_cgroup_clear_mc() up_read(&mmap_sem) We can cause deadlock at (2) because we've already aquire the mmap_sem at (1). But the commit itself is necessary to fix deadlocks which have existed before the commit like: Ex.1) move charge | try charge --------------------------------------+------------------------------ mem_cgroup_can_attach() | down_write(&mmap_sem) mc.moving_task = current | .. mem_cgroup_precharge_mc() | __mem_cgroup_try_charge() mem_cgroup_count_precharge() | prepare_to_wait() down_read(&mmap_sem) | if (mc.moving_task) -> cannot aquire the lock | -> true | schedule() | -> move charge should wake it up Ex.2) move charge | try charge --------------------------------------+------------------------------ mem_cgroup_can_attach() | mc.moving_task = current | mem_cgroup_precharge_mc() | mem_cgroup_count_precharge() | down_read(&mmap_sem) | .. | up_read(&mmap_sem) | | down_write(&mmap_sem) mem_cgroup_move_task() | .. mem_cgroup_move_charge() | __mem_cgroup_try_charge() down_read(&mmap_sem) | prepare_to_wait() -> cannot aquire the lock | if (mc.moving_task) | -> true | schedule() | -> move charge should wake it up This patch fixes all of these problems by: 1. revert the commit. 2. To fix the Ex.1, we set mc.moving_task after mem_cgroup_count_precharge() has released the mmap_sem. 3. To fix the Ex.2, we use down_read_trylock() instead of down_read() in mem_cgroup_move_charge() and, if it has failed to aquire the lock, cancel all extra charges, wake up all waiters, and retry trylock. Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Reported-by: Ben Blum <bblum@andrew.cmu.edu> Cc: Miao Xie <miaox@cn.fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Paul Menage <menage@google.com> Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memcontrol.c84
1 files changed, 49 insertions, 35 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1b44ad64f281..c339d7431bda 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -292,7 +292,6 @@ static struct move_charge_struct {
unsigned long moved_charge;
unsigned long moved_swap;
struct task_struct *moving_task; /* a task moving charges */
- struct mm_struct *mm;
wait_queue_head_t waitq; /* a waitq for other context */
} mc = {
.lock = __SPIN_LOCK_UNLOCKED(mc.lock),
@@ -4681,7 +4680,7 @@ static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
unsigned long precharge;
struct vm_area_struct *vma;
- /* We've already held the mmap_sem */
+ down_read(&mm->mmap_sem);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
struct mm_walk mem_cgroup_count_precharge_walk = {
.pmd_entry = mem_cgroup_count_precharge_pte_range,
@@ -4693,6 +4692,7 @@ static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
walk_page_range(vma->vm_start, vma->vm_end,
&mem_cgroup_count_precharge_walk);
}
+ up_read(&mm->mmap_sem);
precharge = mc.precharge;
mc.precharge = 0;
@@ -4702,10 +4702,15 @@ static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
static int mem_cgroup_precharge_mc(struct mm_struct *mm)
{
- return mem_cgroup_do_precharge(mem_cgroup_count_precharge(mm));
+ unsigned long precharge = mem_cgroup_count_precharge(mm);
+
+ VM_BUG_ON(mc.moving_task);
+ mc.moving_task = current;
+ return mem_cgroup_do_precharge(precharge);
}
-static void mem_cgroup_clear_mc(void)
+/* cancels all extra charges on mc.from and mc.to, and wakes up all waiters. */
+static void __mem_cgroup_clear_mc(void)
{
struct mem_cgroup *from = mc.from;
struct mem_cgroup *to = mc.to;
@@ -4740,23 +4745,28 @@ static void mem_cgroup_clear_mc(void)
PAGE_SIZE * mc.moved_swap);
}
/* we've already done mem_cgroup_get(mc.to) */
-
mc.moved_swap = 0;
}
- if (mc.mm) {
- up_read(&mc.mm->mmap_sem);
- mmput(mc.mm);
- }
+ memcg_oom_recover(from);
+ memcg_oom_recover(to);
+ wake_up_all(&mc.waitq);
+}
+
+static void mem_cgroup_clear_mc(void)
+{
+ struct mem_cgroup *from = mc.from;
+
+ /*
+ * we must clear moving_task before waking up waiters at the end of
+ * task migration.
+ */
+ mc.moving_task = NULL;
+ __mem_cgroup_clear_mc();
spin_lock(&mc.lock);
mc.from = NULL;
mc.to = NULL;
spin_unlock(&mc.lock);
- mc.moving_task = NULL;
- mc.mm = NULL;
mem_cgroup_end_move(from);
- memcg_oom_recover(from);
- memcg_oom_recover(to);
- wake_up_all(&mc.waitq);
}
static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
@@ -4778,38 +4788,23 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
return 0;
/* We move charges only when we move a owner of the mm */
if (mm->owner == p) {
- /*
- * We do all the move charge works under one mmap_sem to
- * avoid deadlock with down_write(&mmap_sem)
- * -> try_charge() -> if (mc.moving_task) -> sleep.
- */
- down_read(&mm->mmap_sem);
-
VM_BUG_ON(mc.from);
VM_BUG_ON(mc.to);
VM_BUG_ON(mc.precharge);
VM_BUG_ON(mc.moved_charge);
VM_BUG_ON(mc.moved_swap);
- VM_BUG_ON(mc.moving_task);
- VM_BUG_ON(mc.mm);
-
mem_cgroup_start_move(from);
spin_lock(&mc.lock);
mc.from = from;
mc.to = mem;
- mc.precharge = 0;
- mc.moved_charge = 0;
- mc.moved_swap = 0;
spin_unlock(&mc.lock);
- mc.moving_task = current;
- mc.mm = mm;
+ /* We set mc.moving_task later */
ret = mem_cgroup_precharge_mc(mm);
if (ret)
mem_cgroup_clear_mc();
- /* We call up_read() and mmput() in clear_mc(). */
- } else
- mmput(mm);
+ }
+ mmput(mm);
}
return ret;
}
@@ -4898,7 +4893,19 @@ static void mem_cgroup_move_charge(struct mm_struct *mm)
struct vm_area_struct *vma;
lru_add_drain_all();
- /* We've already held the mmap_sem */
+retry:
+ if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
+ /*
+ * Someone who are holding the mmap_sem might be waiting in
+ * waitq. So we cancel all extra charges, wake up all waiters,
+ * and retry. Because we cancel precharges, we might not be able
+ * to move enough charges, but moving charge is a best-effort
+ * feature anyway, so it wouldn't be a big problem.
+ */
+ __mem_cgroup_clear_mc();
+ cond_resched();
+ goto retry;
+ }
for (vma = mm->mmap; vma; vma = vma->vm_next) {
int ret;
struct mm_walk mem_cgroup_move_charge_walk = {
@@ -4917,6 +4924,7 @@ static void mem_cgroup_move_charge(struct mm_struct *mm)
*/
break;
}
+ up_read(&mm->mmap_sem);
}
static void mem_cgroup_move_task(struct cgroup_subsys *ss,
@@ -4925,11 +4933,17 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
struct task_struct *p,
bool threadgroup)
{
- if (!mc.mm)
+ struct mm_struct *mm;
+
+ if (!mc.to)
/* no need to move charge */
return;
- mem_cgroup_move_charge(mc.mm);
+ mm = get_task_mm(p);
+ if (mm) {
+ mem_cgroup_move_charge(mm);
+ mmput(mm);
+ }
mem_cgroup_clear_mc();
}
#else /* !CONFIG_MMU */