[PATCH 9/X] uprobes: introduce UTASK_SSTEP_ACK state

[Oleg Nesterov]

Introduce the new state, UTASK_SSTEP_ACK. uprobe_post_notifier()
sets this state like uprobe_bkpt_notifier() sets UTASK_BP_HIT.

Change uprobe_notify_resume() to always do the post_xol() logic
if state != UTASK_BP_HIT and WARN() if the utask->state is wrong.

This makes the state transitions more explicit. The current code
returns silently if, say, state == UTASK_RUNNING. But this must
not happen, we should complain in this case. And, with the new
state we know for sure that DIE_DEBUG was triggered.
---
 include/linux/uprobes.h |    3 ++-
 kernel/uprobes.c        |   15 ++++++++-------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index a407d17..1591c7c 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -74,7 +74,8 @@ struct uprobe {
 enum uprobe_task_state {
 	UTASK_RUNNING,
 	UTASK_BP_HIT,
-	UTASK_SSTEP
+	UTASK_SSTEP,
+	UTASK_SSTEP_ACK,
 };
 
 /*
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 135b9a2..5fd72b8 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1365,10 +1365,13 @@ void uprobe_notify_resume(struct pt_regs *regs)
 		else
 			/* Cannot Singlestep; re-execute the instruction. */
 			goto cleanup_ret;
-	} else if (utask->state == UTASK_SSTEP) {
+	} else {
 		u = utask->active_uprobe;
 
-		post_xol(u, regs);	/* TODO: check result? */
+		if (utask->state == UTASK_SSTEP_ACK)
+			post_xol(u, regs);	/* TODO: check result? */
+		else
+			WARN_ON_ONCE(1);
 
 		put_uprobe(u);
 		utask->active_uprobe = NULL;
@@ -1416,15 +1419,13 @@ int uprobe_bkpt_notifier(struct pt_regs *regs)
  */
 int uprobe_post_notifier(struct pt_regs *regs)
 {
-	struct uprobe *uprobe;
-	struct uprobe_task *utask;
+	struct uprobe_task *utask = current->utask;
 
-	if (!current->mm || !current->utask || !current->utask->active_uprobe)
+	if (!current->mm || !utask || !utask->active_uprobe)
 		/* task is currently not uprobed */
 		return 0;
 
-	utask = current->utask;
-	uprobe = utask->active_uprobe;
+	utask->state = UTASK_SSTEP_ACK;
 	set_thread_flag(TIF_UPROBE);
 	return 1;
 }
-- 
1.5.5.1


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