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SubjectRe: [RFC][PATCH 1/2] printk: lock console_sem before we unregister boot consoles
On (04/24/19 16:49), Petr Mladek wrote:
> > + if (bcon && (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) {
> > + console_lock();
> > + /*
> > + * We need to iterate through all boot consoles, to make
> > * sure we print everything out, before we unregister them.
> > */
>
> I wondered if moving the console locking could break the above
> statement.
>
> It seems that the comment has been invalid since the commit
> 8259cf4342029aad37660e ("printk: Ensure that "console
> enabled" messages are printed on the console").

That's very interesting. Yes, you are right, the comment is a
leftover. printk used to iterate consoles twice before
8259cf4342029aad37660e

/* we need to iterate through twice, to make sure we print
* everything out, before we unregister the console(s)
*/
printk(KERN_INFO "console handover:");
for_each_console(bcon)
printk("boot [%s%d] ", bcon->name, bcon->index);

printk(" -> real [%s%d]\n", newcon->name, newcon->index);
for_each_console(bcon)
unregister_console(bcon);

But 8259cf4342029aad37660e has changed that and has made comment
invalid.

> Could we remove it in this patch? It touches it indirectly anyway.

Sure we can.

We also can take extra care of pr_info("%sconsole [%s%d] enabled\n".
Right now we do

...
console_unlock();
console_sysfs_notify();

pr_info("%sconsole [%s%d] enabled\n",....


But we can simply move that pr_info() a bit up:

pr_info("%sconsole [%s%d] enabled\n",
console_unlock();
console_sysfs_notify();


So the message will be printed on all consoles.

---

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c2bccf58d03e..981eb6c27cdb 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2813,8 +2813,6 @@ void register_console(struct console *newcon)
exclusive_console_stop_seq = console_seq;
logbuf_unlock_irqrestore(flags);
}
- console_unlock();
- console_sysfs_notify();

/*
* By unregistering the bootconsoles after we enable the real console
@@ -2827,6 +2825,9 @@ void register_console(struct console *newcon)
(newcon->flags & CON_BOOT) ? "boot" : "" ,
newcon->name, newcon->index);

+ console_unlock();
+ console_sysfs_notify();
+
if (keep_bootcon)
return;

---
> Otherwise, the patch looks fine to me:
>
> Reviewed-by: Petr Mladek <pmladek@suse.com>

Thanks!

-ss

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