coredump: kill mm->core_done

Now that we have core_state->dumper list we can use it to wake up the
sub-threads waiting for the coredump completion.

This uglifies the code and .text grows by 47 bytes, but otoh mm_struct
lessens by sizeof(struct completion).  Also, with this change we can
decouple exit_mm() from the coredumping code.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 30 insertions, 7 deletions

diff --git a/fs/exec.c b/fs/exec.c
index fe2873b8037f..bff43aeb235e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1602,7 +1602,6 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
         struct completion *vfork_done;
         int core_waiters;
 
-        init_completion(&mm->core_done);
         init_completion(&core_state->startup);
         core_state->dumper.task = tsk;
         core_state->dumper.next = NULL;
@@ -1628,6 +1627,27 @@ fail:
         return core_waiters;
 }
 
+static void coredump_finish(struct mm_struct *mm)
+{
+        struct core_thread *curr, *next;
+        struct task_struct *task;
+
+        next = mm->core_state->dumper.next;
+        while ((curr = next) != NULL) {
+                next = curr->next;
+                task = curr->task;
+                /*
+                 * see exit_mm(), curr->task must not see
+                 * ->task == NULL before we read ->next.
+                 */
+                smp_mb();
+                curr->task = NULL;
+                wake_up_process(task);
+        }
+
+        mm->core_state = NULL;
+}
+
 /*
  * set_dumpable converts traditional three-value dumpable to two flags and
  * stores them into mm->flags.  It modifies lower two bits of mm->flags, but
@@ -1812,8 +1832,7 @@ fail_unlock:
                 argv_free(helper_argv);
 
         current->fsuid = fsuid;
-        complete_all(&mm->core_done);
-        mm->core_state = NULL;
+        coredump_finish(mm);
 fail:
         return retval;
 }
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4d0d0abc79fe..746f975b58ef 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -229,9 +229,7 @@ struct mm_struct {
 
         unsigned long flags; /* Must use atomic bitops to access the bits */
 
-        /* coredumping support */
-        struct core_state *core_state;
-        struct completion core_done;
+        struct core_state *core_state; /* coredumping support */
 
         /* aio bits */
         rwlock_t                ioctx_list_lock;        /* aio lock */
diff --git a/kernel/exit.c b/kernel/exit.c
index b66f0d55c791..8a4d4d12e294 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -691,7 +691,13 @@ static void exit_mm(struct task_struct * tsk)
                 if (atomic_dec_and_test(&core_state->nr_threads))
                         complete(&core_state->startup);
 
-                wait_for_completion(&mm->core_done);
+                for (;;) {
+                        set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+                        if (!self.task) /* see coredump_finish() */
+                                break;
+                        schedule();
+                }
+                __set_task_state(tsk, TASK_RUNNING);
                 down_read(&mm->mmap_sem);
         }
         atomic_inc(&mm->mm_count);