linux-kernel - Re: [PATCH] printk: Update @console_may_schedule in console_trylock

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Date: Mon, 26 Feb 2024 17:47:18 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: John Ogness <john.ogness@...utronix.de>, <pmladek@...e.com>,
        <rostedt@...dmis.org>, <senozhatsky@...omium.org>
CC: <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] printk: Update @console_may_schedule in
 console_trylock_spinning()



On 2/26/2024 5:31 PM, John Ogness wrote:
> console_trylock_spinning() may takeover the console lock from a
> schedulable context. Update @console_may_schedule to make sure it
> reflects a trylock acquire.
> 
> Reported-by: Mukesh Ojha <quic_mojha@...cinc.com>
> Link: https://lore.kernel.org/lkml/20240222090538.23017-1-quic_mojha@quicinc.com
> Fixes: dbdda842fe96 ("printk: Add console owner and waiter logic to load balance console writes")
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Thanks for prompt response..

Yes, this looks fine..
As spinning code runs with preemption disabled context
and should reset the console_may_schedule to 0 .

what if console_trylock_spinning() gets the lock which makes 
console_may_schedule =1 and it is still schedulable ?

-Mukesh

> ---
>   kernel/printk/printk.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 1685a71f3f71..1612b50b2374 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2020,6 +2020,12 @@ static int console_trylock_spinning(void)
>   	 */
>   	mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
>   
> +	/*
> +	 * Update @console_may_schedule for trylock because the previous
> +	 * owner may have been schedulable.
> +	 */
> +	console_may_schedule = 0;
> +
>   	return 1;
>   }
>   
> 
> base-commit: e7081d5a9d976b84f61f497316d7c940a4a2e67a