Messages in this thread | | | Date | Fri, 21 Oct 2022 11:25:14 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH printk v2 05/38] printk: use console_is_enabled() |
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On Wed 2022-10-19 17:01:27, John Ogness wrote: > Replace (console->flags & CON_ENABLED) usage with console_is_enabled(). > > Signed-off-by: John Ogness <john.ogness@linutronix.de> > --- > kernel/printk/printk.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index e8a56056cd50..7ff2fc75fc3b 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2658,7 +2658,7 @@ static bool abandon_console_lock_in_panic(void) > */ > static inline bool console_is_usable(struct console *con) > { > - if (!(con->flags & CON_ENABLED)) > + if (!console_is_enabled(con)) > return false;
This allows to use console_is_usable() without synchronization against modification of the state. I guess that it will be needed for the printk kthreads. But it is not needed at the moment.
We should document why it is needed and why it is safe.
> > if (!con->write) > @@ -2944,7 +2944,7 @@ void console_unblank(void) > console_locked = 1; > console_may_schedule = 0; > for_each_console(c) > - if ((c->flags & CON_ENABLED) && c->unblank) > + if (console_is_enabled(c) && c->unblank) > c->unblank(); > console_unlock();
The reading of the flag is actually synchronized against modifications here. I guess that we need this because c->unblank() probably is not safe against other operations with the console, e.g. c->write().
Well, it probably does not matter if reading of CON_ENABLED flag is serialized against modifications. So, it is perfectly fine to use the "racy" function.
> @@ -3098,7 +3098,7 @@ static int try_enable_preferred_console(struct console *newcon, > * without matching. Accept the pre-enabled consoles only when match() > * and setup() had a chance to be called. > */ > - if (newcon->flags & CON_ENABLED && c->user_specified == user_specified) > + if (console_is_enabled(newcon) && (c->user_specified == user_specified))
This is not racy because newcon is not in console_list at this point. So that the state can't be modified by another callers.
Anyway, it is not explicitly synchronized, so we need to use console_is_enabled with data_race() annotation.
> return 0; > > return -ENOENT;
Best Regards, Petr
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