Merge tag 'v4.14-rc2' into next-general

Linux 4.14-rc2

Sync to v4.14-rc2 for security subsystem developers to track.

1 files changed, 10 insertions, 14 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 9e8b4f030c1c..99736e026712 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -495,11 +495,12 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 	}
 
 	/*
-	 * increase mm_users only after we know we will reap something so
-	 * that the mmput_async is called only when we have reaped something
-	 * and delayed __mmput doesn't matter that much
+	 * MMF_OOM_SKIP is set by exit_mmap when the OOM reaper can't
+	 * work on the mm anymore. The check for MMF_OOM_SKIP must run
+	 * under mmap_sem for reading because it serializes against the
+	 * down_write();up_write() cycle in exit_mmap().
 	 */
-	if (!mmget_not_zero(mm)) {
+	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
 		up_read(&mm->mmap_sem);
 		trace_skip_task_reaping(tsk->pid);
 		goto unlock_oom;
@@ -542,12 +543,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 			K(get_mm_counter(mm, MM_SHMEMPAGES)));
 	up_read(&mm->mmap_sem);
 
-	/*
-	 * Drop our reference but make sure the mmput slow path is called from a
-	 * different context because we shouldn't risk we get stuck there and
-	 * put the oom_reaper out of the way.
-	 */
-	mmput_async(mm);
 	trace_finish_task_reaping(tsk->pid);
 unlock_oom:
 	mutex_unlock(&oom_lock);
@@ -824,7 +819,8 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 
 	/*
 	 * If the task is already exiting, don't alarm the sysadmin or kill
-	 * its children or threads, just set TIF_MEMDIE so it can die quickly
+	 * its children or threads, just give it access to memory reserves
+	 * so it can die quickly
 	 */
 	task_lock(p);
 	if (task_will_free_mem(p)) {
@@ -889,9 +885,9 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 	count_memcg_event_mm(mm, OOM_KILL);
 
 	/*
-	 * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
-	 * the OOM victim from depleting the memory reserves from the user
-	 * space under its control.
+	 * We should send SIGKILL before granting access to memory reserves
+	 * in order to prevent the OOM victim from depleting the memory
+	 * reserves from the user space under its control.
 	 */
 	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
 	mark_oom_victim(victim);