Re: [PATCH printk 11/18] printk: Convert console_drivers list to hlist

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On 9/30/22 16:20, Petr Mladek wrote:
On Sat 2022-09-24 02:10:47, John Ogness wrote:
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Replace the open coded single linked list with a hlist so a conversion to
SRCU protected list walks can reuse the existing primitives.

--- a/arch/parisc/kernel/pdc_cons.c
+++ b/arch/parisc/kernel/pdc_cons.c
@@ -272,15 +267,17 @@ void pdc_console_restart(bool hpmc)
  	if (pdc_console_initialized)
  		return;

-	if (!hpmc && console_drivers)
+	if (!hpmc && !hlist_empty(&console_list))
  		return;

  	/* If we've already seen the output, don't bother to print it again */
-	if (console_drivers != NULL)
+	if (!hlist_empty(&console_list))
  		pdc_cons.flags &= ~CON_PRINTBUFFER;

-	while ((console = console_drivers) != NULL)
-		unregister_console(console_drivers);
+	while (!hlist_empty(&console_list)) {
+		unregister_console(READ_ONCE(hlist_entry(console_list.first,
+							 struct console, node)));

The READ_ONCE() is in a wrong place. This is why it did not compile.
It should be:

		unregister_console(hlist_entry(READ_ONCE(console_list.first),
						struct console,
						node));

I know that it is all hope for good. But there is also a race between
the hlist_empty() and hlist_entry().

I wonder if pdc_console() is still needed as it is today.
When this was written, early_console and such didn't worked for parisc
as it should. That's proably why we have this register/unregister in here.

Would it make sense, and would we gain something for this printk-series,
if I'd try to convert pdc_console to a standard earlycon or earlyprintk device?

Helge




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