1 files changed, 55 insertions, 88 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1c52ddbc839b..34d3ca9572d6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -866,6 +866,7 @@ 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 +874,7 @@ 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;
 }
 
@@ -2159,110 +2161,59 @@ 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 +2222,25 @@ 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 +2249,9 @@ 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 +2665,9 @@ 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
@@ -2801,6 +2766,8 @@ done:
         return 0;
 nomem:
         *ptr = NULL;
+        if (gfp_mask & __GFP_NOFAIL)
+                return 0;
         return -ENOMEM;
 bypass:
         *ptr = root_mem_cgroup;