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SubjectRe: [RFC][PATCH 1/2] printk: lock console_sem before we unregister boot consoles
On Thu 2019-04-25 12:52:33, Sergey Senozhatsky wrote:
> 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.

Great idea!

It would deserve a separate patch that moves the pr_info()
and removes the invalid comment.

Actually, the pr_info() would deserve a comment explaining
why it should be called before console_unlock().

Best Regards,
Petr

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