[PATCH] serdev: Do not call .receive_buf() callback recursively

[Andrey Smirnov <andrew.smirnov@gmail.com>]

Code implementing .receive_buf() callback can potentially call
serdev_device_write(), which will call serdev_device_poller(). We need
to make sure that such a call is a no-op in order to prevent
corrupting shared data buffer as well as breaking .receive_buf
callback that most likely does not expect that to happen.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
---
 common/serdev.c  | 6 ++++++
 include/serdev.h | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/common/serdev.c b/common/serdev.c
index 4a6dbefe6..3e0da0846 100644
--- a/common/serdev.c
+++ b/common/serdev.c
@@ -9,6 +9,10 @@ static void serdev_device_poller(void *context)
 	unsigned char *buf = serdev->buf;
 	int ret, len;
 
+	if (serdev->locked)
+		return;
+
+	serdev->locked = true;
 	/*
 	 * Since this callback is a part of poller infrastructure we
 	 * want to use _non_interruptible version of the function
@@ -37,6 +41,8 @@ static void serdev_device_poller(void *context)
 	} else {
 		poller_async_cancel(&serdev->poller);
 	}
+
+	serdev->locked = false;
 }
 
 static int serdev_device_set_polling_interval(struct param_d *param, void *serdev)
diff --git a/include/serdev.h b/include/serdev.h
index f5d34f527..29030538e 100644
--- a/include/serdev.h
+++ b/include/serdev.h
@@ -14,6 +14,7 @@
  * @poller		Async poller used to poll this serdev
  * @polling_interval:	Async poller periodicity
  * @polling_window:	Duration of a single busy loop poll
+ * @locked:		Lock to prevent recursive polling
  * @receive_buf:	Function called with data received from device;
  *			returns number of bytes accepted;
  */
@@ -24,6 +25,7 @@ struct serdev_device {
 	struct poller_async poller;
 	uint64_t polling_interval;
 	uint64_t polling_window;
+	bool locked;
 
 	int (*receive_buf)(struct serdev_device *, const unsigned char *,
 			   size_t);
-- 
2.21.0


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