Re: [PATCH resend] serial_core: Fix pm imbalance on unbind

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Geert,

On 03/21/2014 09:23 AM, Geert Uytterhoeven wrote:
Hi Peter,

On Fri, Mar 21, 2014 at 2:06 PM, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote:
@@ -2681,10 +2683,12 @@ int uart_remove_one_port(struct uart_driver *drv,
struct uart_port *uport)
         }

         /*
-        * If the port is used as a console, unregister it
+        * If the port is used as a console, unregister it, and power it
down
          */
-       if (uart_console(uport))
+       if (uart_console(uport)) {
                 unregister_console(uport->cons);
+               uart_change_pm(state, UART_PM_STATE_OFF);

Won't this power off the port while tty consoles may still be open?

I didn't see that actually happening.

Ok, but I still think this isn't right. See below.

I think the right thing here is to unregister_console then set uport->cons =
NULL

[uport->cons is properly reassigned when/if a port is re-added via
uart_add_one_port()).]

But indeed, for concistency/symmetry uport->state and uport->cons
should be resend, but that's something separate.

I don't see this as being a "looks good" problem; I see this as being
"what's the right way to teardown a uart device that's going away when
a tty console is running on it", and there are too many problems with
uart_remove_one_port() doing:

     state->uart_port = NULL

to keep with that solution.

Then, uart_close() will power off the port when all ttys using the port have
been closed.

uart_close() won't get that far, so uart_change_pm() won't be called.

And this is the central problem: uart_close() must complete normally
if a tty console is still running on a device.

For example, if uart_shutdown() isn't getting called, then who's freeing
the ring buffer page?


See also https://lkml.org/lkml/2014/3/10/651, and my workaround for the
crash https://lkml.org/lkml/2014/3/17/231.

See my comments to the v2 patch there.

Regards,
Peter Hurley
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux PPP]     [Linux FS]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Linmodem]     [Device Mapper]     [Linux Kernel for ARM]

  Powered by Linux