On 5/31/2025 3:20 PM, Greg Kroah-Hartman wrote:

On Fri, May 30, 2025 at 04:34:49PM +0800, Xin Chen wrote:

quoted

On 5/29/2025 5:41 PM, Greg Kroah-Hartman wrote:

quoted

On Thu, May 29, 2025 at 11:07:25AM +0200, Greg Kroah-Hartman wrote:

quoted

On Fri, May 23, 2025 at 10:52:27AM +0800, Xin Chen wrote:

quoted

On 5/14/2025 5:14 PM, Xin Chen wrote:

quoted

On 5/8/2025 5:41 PM, Greg Kroah-Hartman wrote:

quoted

On Thu, May 08, 2025 at 05:29:18PM +0800, Xin Chen wrote:

quoted

On 4/30/2025 7:40 PM, Greg Kroah-Hartman wrote:

quoted

On Wed, Apr 30, 2025 at 07:16:17PM +0800, Xin Chen wrote:

quoted

When ttyport_open() fails to initialize a tty device, serport->tty is not

--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c

@@ -88,6 +88,10 @@ static void ttyport_write_flush(struct serdev_controller *ctrl)
 {
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
+	if (!tty) {
+		dev_err(&ctrl->dev, "tty is null\n");
+		return;
+	}

What prevents tty from going NULL right after you just checked this?

First sorry for reply so late for I have a long statutory holidays.
Maybe I don't get your point. From my side, there is nothing to prevent it.
Check here is to avoid code go on if tty is NULL.

Yes, but the problem is, serport->tty could change to be NULL right
after you check it, so you have not removed the real race that can
happen here.  There is no lock, so by adding this check you are only
reducing the risk of the problem happening, not actually fixing the
issue so that it will never happen.

Please fix it so that this can never happen.

Actually I have never thought the race condition issue since the crash I met is
not caused by race condition. It's caused due to Bluetooth driver call
ttyport_close() after ttyport_open() failed. This two action happen one after
another in one thread and it seems impossible to have race condition. And with
my fix the crash doesn't happen again in several test of same case.

Let me introduce the complete process for you:
  1) hci_dev_open_sync()->
hci_dev_init_sync()->hci_dev_setup_sync()->hdev->setup()(hci_uart_setup)->qca_setup(),
here in qca_setup(), qca_read_soc_version() fails and goto out, then calls
serdev_device_close() to close tty normally. And then call serdev_device_open()
to retry.

Wait, what?  Why is qca_read_soc_version() failing?  

Actually I have not root cause why qca_read_soc_version() fails of
__hci_cmd_sync_ev(). It may be relative to FW issue.

Please start there, don't you want to know why things are failing?

quoted

quoted

Why are you retrying multiple times until either you run out of attempts?  

This is a retry mechanism. I find the reason in the change commit message
"Currently driver only retries to download FW if FW downloading
is failed. Sometimes observed command timeout for version request
command, if this happen on some platforms during boot time, then
a reboot is needed to turn ON BT. Instead to avoid a reboot, now
extended retry logic for version request command too."

quoted

Why are you closing the port and then opening it again right away? 

This is a retry mechanism as above said. Do you mean there should be a gap
between close and open? The change owner maybe don't think about this issue.

Why are you calling close/open at all?  Why does that do anything?
Doesn't that feel wrong?

Again, please root-cause the failure, don't try to paper over it by
loads of looping and odd open/close attempts that are not understood and
seem to actually cause other types of crashes :)

quoted

quoted

What close/open pair seems totally unnecessary, why do that at all?

If I read that function qca_setup(), it can NEVER detect if a failure
really happened (i.e. if it does run out of retries, you just plow on
and keep going and keep on registering things and THEN return an error
for some reason.

In other words, the error handling in qca_setup() is very suspect, why
not fix all of that up first?

qca_read_soc_version() in qca_setup() can detect whether the hci_dev is set up
successfully. If if fails then a failure happens.
You mean I should fix why qca_read_soc_version() fails?

Yes, why wouldn't you want to do that?

Yeah you are right. I will try to root cause the qca read version issue and fix
it first. Thanks very much!

Xin