[PATCH] c/r: threads sync on restart (fix regression from commit afbe522c...)

[Oren Laadan]

Initialize the new member signal->restart_count in copy_signal().

The lack of which in commit afbe522ccf6b1deb5edfc01a00becfe6ee325d0c,
c/r: let entire thread group in sys_restart before restoring a thread,
can cause run-pthreads1.sh test failure.

In this patch are two other small cleanups:

1) In post_restore_task() test if current->checkpoint_data is valid,
and return immediately if not (meaning restart failed early).

2) Replace two instances of DECLARE_WAIT_QUEUE_HEAD(waitq) with
DECLARE_WAIT_QUEUE_HEAD_ONSTACK(waitq), to please the lockdep checked.

Signed-off-by: Oren Laadan <orenl at cs.columbia.edu>
---
 checkpoint/process.c |    4 ++++
 checkpoint/restart.c |    4 ++--
 kernel/fork.c        |    4 ++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/checkpoint/process.c b/checkpoint/process.c
index c2832fe..424f688 100644
--- a/checkpoint/process.c
+++ b/checkpoint/process.c
@@ -847,6 +847,10 @@ int pre_restore_task(struct ckpt_ctx *ctx)
 /* pre_restore_task - prepare the task for restore */
 void post_restore_task(struct ckpt_ctx *ctx)
 {
+	/* can happen if restart failed early */
+	if (!current->checkpoint_data)
+		return;
+
 	/* only now is it safe to unblock the restored task's signals */
 	sigprocmask(SIG_SETMASK, &current->checkpoint_data->blocked, NULL);
 
diff --git a/checkpoint/restart.c b/checkpoint/restart.c
index b2dc139..3a58a76 100644
--- a/checkpoint/restart.c
+++ b/checkpoint/restart.c
@@ -821,7 +821,7 @@ static int wait_task_sync(struct ckpt_ctx *ctx)
 /* grabs a reference to the @ctx on success; caller should free */
 static struct ckpt_ctx *wait_checkpoint_ctx(void)
 {
-	DECLARE_WAIT_QUEUE_HEAD(waitq);
+	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(waitq);
 	struct ckpt_ctx *ctx;
 	int ret;
 
@@ -912,7 +912,7 @@ static int wait_sync_threads(void)
 			wake_up_process(p);
 		read_unlock(&tasklist_lock);
 	} else {
-		DECLARE_WAIT_QUEUE_HEAD(waitq);
+		DECLARE_WAIT_QUEUE_HEAD_ONSTACK(waitq);
 		ret = wait_event_interruptible(waitq, !atomic_read(count));
 	}
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 0e226f5..04dffe9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -865,6 +865,10 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 
 	tty_audit_fork(sig);
 
+#ifdef CONFIG_CHECKPOINT
+	atomic_set(&sig->restart_count, 0);
+#endif
+
 	return 0;
 }
 
-- 
1.6.0.4