1 files changed, 79 insertions, 117 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1c52ddb..13b9d0f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -54,6 +54,7 @@
 #include <linux/page_cgroup.h>
 #include <linux/cpu.h>
 #include <linux/oom.h>
+#include <linux/lockdep.h>
 #include "internal.h"
 #include <net/sock.h>
 #include <net/ip.h>
@@ -866,6 +867,7 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
 	unsigned long val = 0;
 	int cpu;
 
+	get_online_cpus();
 	for_each_online_cpu(cpu)
 		val += per_cpu(memcg->stat->events[idx], cpu);
 #ifdef CONFIG_HOTPLUG_CPU
@@ -873,6 +875,7 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
 	val += memcg->nocpu_base.events[idx];
 	spin_unlock(&memcg->pcp_counter_lock);
 #endif
+	put_online_cpus();
 	return val;
 }
 
@@ -2044,6 +2047,12 @@ static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
 	return total;
 }
 
+#ifdef CONFIG_LOCKDEP
+static struct lockdep_map memcg_oom_lock_dep_map = {
+	.name = "memcg_oom_lock",
+};
+#endif
+
 static DEFINE_SPINLOCK(memcg_oom_lock);
 
 /*
@@ -2081,7 +2090,8 @@ static bool mem_cgroup_oom_trylock(struct mem_cgroup *memcg)
 			}
 			iter->oom_lock = false;
 		}
-	}
+	} else
+		mutex_acquire(&memcg_oom_lock_dep_map, 0, 1, _RET_IP_);
 
 	spin_unlock(&memcg_oom_lock);
 
@@ -2093,6 +2103,7 @@ static void mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
 	struct mem_cgroup *iter;
 
 	spin_lock(&memcg_oom_lock);
+	mutex_release(&memcg_oom_lock_dep_map, 1, _RET_IP_);
 	for_each_mem_cgroup_tree(iter, memcg)
 		iter->oom_lock = false;
 	spin_unlock(&memcg_oom_lock);
@@ -2159,110 +2170,59 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
 		memcg_wakeup_oom(memcg);
 }
 
-/*
- * try to call OOM killer
- */
 static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
 {
-	bool locked;
-	int wakeups;
-
 	if (!current->memcg_oom.may_oom)
 		return;
-
-	current->memcg_oom.in_memcg_oom = 1;
-
 	/*
-	 * As with any blocking lock, a contender needs to start
-	 * listening for wakeups before attempting the trylock,
-	 * otherwise it can miss the wakeup from the unlock and sleep
-	 * indefinitely.  This is just open-coded because our locking
-	 * is so particular to memcg hierarchies.
+	 * We are in the middle of the charge context here, so we
+	 * don't want to block when potentially sitting on a callstack
+	 * that holds all kinds of filesystem and mm locks.
+	 *
+	 * Also, the caller may handle a failed allocation gracefully
+	 * (like optional page cache readahead) and so an OOM killer
+	 * invocation might not even be necessary.
+	 *
+	 * That's why we don't do anything here except remember the
+	 * OOM context and then deal with it at the end of the page
+	 * fault when the stack is unwound, the locks are released,
+	 * and when we know whether the fault was overall successful.
 	 */
-	wakeups = atomic_read(&memcg->oom_wakeups);
-	mem_cgroup_mark_under_oom(memcg);
-
-	locked = mem_cgroup_oom_trylock(memcg);
-
-	if (locked)
-		mem_cgroup_oom_notify(memcg);
-
-	if (locked && !memcg->oom_kill_disable) {
-		mem_cgroup_unmark_under_oom(memcg);
-		mem_cgroup_out_of_memory(memcg, mask, order);
-		mem_cgroup_oom_unlock(memcg);
-		/*
-		 * There is no guarantee that an OOM-lock contender
-		 * sees the wakeups triggered by the OOM kill
-		 * uncharges.  Wake any sleepers explicitely.
-		 */
-		memcg_oom_recover(memcg);
-	} else {
-		/*
-		 * A system call can just return -ENOMEM, but if this
-		 * is a page fault and somebody else is handling the
-		 * OOM already, we need to sleep on the OOM waitqueue
-		 * for this memcg until the situation is resolved.
-		 * Which can take some time because it might be
-		 * handled by a userspace task.
-		 *
-		 * However, this is the charge context, which means
-		 * that we may sit on a large call stack and hold
-		 * various filesystem locks, the mmap_sem etc. and we
-		 * don't want the OOM handler to deadlock on them
-		 * while we sit here and wait.  Store the current OOM
-		 * context in the task_struct, then return -ENOMEM.
-		 * At the end of the page fault handler, with the
-		 * stack unwound, pagefault_out_of_memory() will check
-		 * back with us by calling
-		 * mem_cgroup_oom_synchronize(), possibly putting the
-		 * task to sleep.
-		 */
-		current->memcg_oom.oom_locked = locked;
-		current->memcg_oom.wakeups = wakeups;
-		css_get(&memcg->css);
-		current->memcg_oom.wait_on_memcg = memcg;
-	}
+	css_get(&memcg->css);
+	current->memcg_oom.memcg = memcg;
+	current->memcg_oom.gfp_mask = mask;
+	current->memcg_oom.order = order;
 }
 
 /**
  * mem_cgroup_oom_synchronize - complete memcg OOM handling
+ * @handle: actually kill/wait or just clean up the OOM state
  *
- * This has to be called at the end of a page fault if the the memcg
- * OOM handler was enabled and the fault is returning %VM_FAULT_OOM.
+ * This has to be called at the end of a page fault if the memcg OOM
+ * handler was enabled.
  *
- * Memcg supports userspace OOM handling, so failed allocations must
+ * Memcg supports userspace OOM handling where failed allocations must
  * sleep on a waitqueue until the userspace task resolves the
  * situation.  Sleeping directly in the charge context with all kinds
  * of locks held is not a good idea, instead we remember an OOM state
  * in the task and mem_cgroup_oom_synchronize() has to be called at
- * the end of the page fault to put the task to sleep and clean up the
- * OOM state.
+ * the end of the page fault to complete the OOM handling.
  *
  * Returns %true if an ongoing memcg OOM situation was detected and
- * finalized, %false otherwise.
+ * completed, %false otherwise.
  */
-bool mem_cgroup_oom_synchronize(void)
+bool mem_cgroup_oom_synchronize(bool handle)
 {
+	struct mem_cgroup *memcg = current->memcg_oom.memcg;
 	struct oom_wait_info owait;
-	struct mem_cgroup *memcg;
+	bool locked;
 
 	/* OOM is global, do not handle */
-	if (!current->memcg_oom.in_memcg_oom)
-		return false;
-
-	/*
-	 * We invoked the OOM killer but there is a chance that a kill
-	 * did not free up any charges.  Everybody else might already
-	 * be sleeping, so restart the fault and keep the rampage
-	 * going until some charges are released.
-	 */
-	memcg = current->memcg_oom.wait_on_memcg;
 	if (!memcg)
-		goto out;
+		return false;
 
-	if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
-		goto out_memcg;
+	if (!handle)
+		goto cleanup;
 
 	owait.memcg = memcg;
 	owait.wait.flags = 0;
@@ -2271,13 +2231,25 @@ bool mem_cgroup_oom_synchronize(void)
 	INIT_LIST_HEAD(&owait.wait.task_list);
 
 	prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
-	/* Only sleep if we didn't miss any wakeups since OOM */
-	if (atomic_read(&memcg->oom_wakeups) == current->memcg_oom.wakeups)
+	mem_cgroup_mark_under_oom(memcg);
+
+	locked = mem_cgroup_oom_trylock(memcg);
+
+	if (locked)
+		mem_cgroup_oom_notify(memcg);
+
+	if (locked && !memcg->oom_kill_disable) {
+		mem_cgroup_unmark_under_oom(memcg);
+		finish_wait(&memcg_oom_waitq, &owait.wait);
+		mem_cgroup_out_of_memory(memcg, current->memcg_oom.gfp_mask,
+					 current->memcg_oom.order);
+	} else {
 		schedule();
-	finish_wait(&memcg_oom_waitq, &owait.wait);
-out_memcg:
-	mem_cgroup_unmark_under_oom(memcg);
-	if (current->memcg_oom.oom_locked) {
+		mem_cgroup_unmark_under_oom(memcg);
+		finish_wait(&memcg_oom_waitq, &owait.wait);
+	}
+
+	if (locked) {
 		mem_cgroup_oom_unlock(memcg);
 		/*
 		 * There is no guarantee that an OOM-lock contender
@@ -2286,10 +2258,9 @@ out_memcg:
 		 */
 		memcg_oom_recover(memcg);
 	}
+cleanup:
+	current->memcg_oom.memcg = NULL;
 	css_put(&memcg->css);
-	current->memcg_oom.wait_on_memcg = NULL;
-out:
-	current->memcg_oom.in_memcg_oom = 0;
 	return true;
 }
 
@@ -2703,6 +2674,9 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 		     || fatal_signal_pending(current)))
 		goto bypass;
 
+	if (unlikely(task_in_memcg_oom(current)))
+		goto bypass;
+
 	/*
 	 * We always charge the cgroup the mm_struct belongs to.
 	 * The mm_struct's mem_cgroup changes on task migration if the
@@ -2800,8 +2774,10 @@ done:
 	*ptr = memcg;
 	return 0;
 nomem:
-	*ptr = NULL;
-	return -ENOMEM;
+	if (!(gfp_mask & __GFP_NOFAIL)) {
+		*ptr = NULL;
+		return -ENOMEM;
+	}
 bypass:
 	*ptr = root_mem_cgroup;
 	return -EINTR;
@@ -3806,8 +3782,7 @@ void mem_cgroup_move_account_page_stat(struct mem_cgroup *from,
 {
 	/* Update stat data for mem_cgroup */
 	preempt_disable();
-	WARN_ON_ONCE(from->stat->count[idx] < nr_pages);
-	__this_cpu_add(from->stat->count[idx], -nr_pages);
+	__this_cpu_sub(from->stat->count[idx], nr_pages);
 	__this_cpu_add(to->stat->count[idx], nr_pages);
 	preempt_enable();
 }
@@ -4983,31 +4958,18 @@ static void mem_cgroup_reparent_charges(struct mem_cgroup *memcg)
 	} while (usage > 0);
 }
 
-/*
- * This mainly exists for tests during the setting of set of use_hierarchy.
- * Since this is the very setting we are changing, the current hierarchy value
- * is meaningless
- */
-static inline bool __memcg_has_children(struct mem_cgroup *memcg)
-{
-	struct cgroup_subsys_state *pos;
-
-	/* bounce at first found */
-	css_for_each_child(pos, &memcg->css)
-		return true;
-	return false;
-}
-
-/*
- * Must be called with memcg_create_mutex held, unless the cgroup is guaranteed
- * to be already dead (as in mem_cgroup_force_empty, for instance).  This is
- * from mem_cgroup_count_children(), in the sense that we don't really care how
- * many children we have; we only need to know if we have any.  It also counts
- * any memcg without hierarchy as infertile.
- */
 static inline bool memcg_has_children(struct mem_cgroup *memcg)
 {
-	return memcg->use_hierarchy && __memcg_has_children(memcg);
+	lockdep_assert_held(&memcg_create_mutex);
+	/*
+	 * The lock does not prevent addition or deletion to the list
+	 * of children, but it prevents a new child from being
+	 * initialized based on this parent in css_online(), so it's
+	 * enough to decide whether hierarchically inherited
+	 * attributes can still be changed or not.
+	 */
+	return memcg->use_hierarchy &&
+		!list_empty(&memcg->css.cgroup->children);
 }
 
 /*
@@ -5087,7 +5049,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
 	 */
 	if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
 				(val == 1 || val == 0)) {
-		if (!__memcg_has_children(memcg))
+		if (list_empty(&memcg->css.cgroup->children))
 			memcg->use_hierarchy = val;
 		else
 			retval = -EBUSY;