linux-kernel - [PATCH 4.4 39/53] binder: Use wake up hint for synchronous transactions.

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Message-Id: <20170828080519.409524726@linuxfoundation.org>
Date:   Mon, 28 Aug 2017 10:05:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Todd Kjos <tkjos@...gle.com>,
        Omprakash Dhyade <odhyade@...eaurora.org>
Subject: [PATCH 4.4 39/53] binder: Use wake up hint for synchronous transactions.

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Riley Andrews <riandrews@...gle.com>

commit 00b40d613352c623aaae88a44e5ded7c912909d7 upstream.

Use wake_up_interruptible_sync() to hint to the scheduler binder
transactions are synchronous wakeups. Disable preemption while waking
to avoid ping-ponging on the binder lock.

Signed-off-by: Todd Kjos <tkjos@...gle.com>
Signed-off-by: Omprakash Dhyade <odhyade@...eaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/android/binder.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1718,8 +1718,12 @@ static void binder_transaction(struct bi
 	list_add_tail(&t->work.entry, target_list);
 	tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
 	list_add_tail(&tcomplete->entry, &thread->todo);
-	if (target_wait)
-		wake_up_interruptible(target_wait);
+	if (target_wait) {
+		if (reply || !(t->flags & TF_ONE_WAY))
+			wake_up_interruptible_sync(target_wait);
+		else
+			wake_up_interruptible(target_wait);
+	}
 	return;
 
 err_get_unused_fd_failed: