mm, oom: remove unnecessary exit_state check

The oom killer scans each process and determines whether it is eligible
for oom kill or whether the oom killer should abort because of
concurrent memory freeing.  It will abort when an eligible process is
found to have TIF_MEMDIE set, meaning it has already been oom killed and
we're waiting for it to exit.

Processes with task->mm == NULL should not be considered because they
are either kthreads or have already detached their memory and killing
them would not lead to memory freeing.  That memory is only freed after
exit_mm() has returned, however, and not when task->mm is first set to
NULL.

Clear TIF_MEMDIE after exit_mm()'s mmput() so that an oom killed process
is no longer considered for oom kill, but only until exit_mm() has
returned.  This was fragile in the past because it relied on
exit_notify() to be reached before no longer considering TIF_MEMDIE
processes.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/exit.c b/kernel/exit.c
index e5c4668f1799d15ce1d527b1e357d795f3d748ea..88c6b3e425834e89943bb1a291a7a350333e3593 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -455,6 +455,7 @@ static void exit_mm(struct task_struct * tsk)
        task_unlock(tsk);
        mm_update_next_owner(mm);
        mmput(mm);
+       clear_thread_flag(TIF_MEMDIE);
 }
 
 /*

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d33aca1552addc67196e47939405befe330f6f13..1e11df8fa7ecaecd274a3d0aaa1fe0aea4bb38ab 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -258,8 +258,6 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
                unsigned long totalpages, const nodemask_t *nodemask,
                bool force_kill)
 {
-       if (task->exit_state)
-               return OOM_SCAN_CONTINUE;
        if (oom_unkillable_task(task, NULL, nodemask))
                return OOM_SCAN_CONTINUE;