Messages in this thread | | | Date | Fri, 18 Feb 2022 10:12:50 +0100 | From | Petr Mladek <> | Subject | wake_up_all: was: Re: [PATCH printk v1 10/13] printk: add kthread console printers |
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On Mon 2022-02-07 20:49:20, John Ogness wrote: > Create a kthread for each console to perform console printing. During > normal operation (@system_state == SYSTEM_RUNNING), the kthread > printers are responsible for all printing on their respective > consoles. > > During non-normal operation, console printing is done as it has been: > within the context of the printk caller or within irq work triggered > by the printk caller. > > Console printers synchronize against each other and against console > lockers by taking the console lock for each message that is printed. > --- > include/linux/console.h | 2 + > kernel/printk/printk.c | 159 +++++++++++++++++++++++++++++++++++++++- > 2 files changed, 159 insertions(+), 2 deletions(-) > > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -3371,7 +3526,7 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work) > } > > if (pending & PRINTK_PENDING_WAKEUP) > - wake_up_interruptible(&log_wait); > + wake_up_interruptible_all(&log_wait);
Good catch. I am curious how this worked so far. It looks like only the first waiter was waken and others had to wait for another new message.
The typical problem with wake_up_interruptible_all() is that it wakes many processes that needs to take the same lock and block each other. There is even a name for this situation but I do not recall it.
My understanding is that wake_up_interruptible() requires that the waken process wakes the next waiter when done. But I do not see it guaranteed for @log_wait wait queue.
Best Regards, Petr
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