[PATCH v6 3.2-rc1 25/28] uprobes: call post_xol() unconditionally

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

Kill sstep_complete(), change uprobe_notify_resume() to use
post_xol() unconditionally.

It is wrong to assume that regs->ip always changes after the step.
rep or jmp/call to self for example. We know that this task has
already done the step, we can rely on DIE_DEBUG notification.

Original-patch-from: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 include/linux/uprobes.h |    3 ++-
 kernel/uprobes.c        |   40 ++++++++++++----------------------------
 2 files changed, 14 insertions(+), 29 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index add5222..70d639c 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 9e73cef..13b1d68 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1316,24 +1316,6 @@ static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs,
 }
 
 /*
- * Verify from Instruction Pointer if singlestep has indeed occurred.
- * If Singlestep has occurred, then do post singlestep fix-ups.
- */
-static bool sstep_complete(struct uprobe *uprobe, struct pt_regs *regs)
-{
-	unsigned long vaddr = instruction_pointer(regs);
-
-	/*
-	 * If we have executed out of line, Instruction pointer
-	 * cannot be same as virtual address of XOL slot.
-	 */
-	if (vaddr == current->utask->xol_vaddr)
-		return false;
-	post_xol(uprobe, regs);
-	return true;
-}
-
-/*
  * uprobe_notify_resume gets called in task context just before returning
  * to userspace.
  *
@@ -1381,17 +1363,18 @@ 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;
-		if (sstep_complete(u, regs)) {
-			put_uprobe(u);
-			utask->active_uprobe = NULL;
-			utask->state = UTASK_RUNNING;
-			user_disable_single_step(current);
-			xol_free_insn_slot(current);
-
-			/* TODO Stop queueing signals. */
-		}
+		if (utask->state == UTASK_SSTEP_ACK)
+			post_xol(u, regs);
+		else
+			WARN_ON_ONCE(1);
+
+		put_uprobe(u);
+		utask->active_uprobe = NULL;
+		utask->state = UTASK_RUNNING;
+		user_disable_single_step(current);
+		xol_free_insn_slot(current);
 	}
 	return;
 
@@ -1441,6 +1424,7 @@ int uprobe_post_notifier(struct pt_regs *regs)
 		/* task is currently not uprobed */
 		return 0;
 
+	utask->state = UTASK_SSTEP_ACK;
 	set_thread_flag(TIF_UPROBE);
 	return 1;
 }

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