linux-kernel - Re: [PATCH] printk: Add atomic context check inside console

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Message-ID: <e5474801-53c1-6bbb-8781-e5cee42d6a90@quicinc.com>
Date: Mon, 26 Feb 2024 15:47:47 +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: Add atomic context check inside console_unlock()



On 2/22/2024 8:23 PM, John Ogness wrote:
> On 2024-02-22, Mukesh Ojha <quic_mojha@...cinc.com> wrote:
>> Situation of schedule while atomic context can happen in a
>> scenario if CPU-Y executing a async probe of ufs and while
>> printing a line it is started spinning for console lock
>> after preemption disable on CPU-Y and later it got the handover
>> of console lock from CPU-X and in console_unlock() it get
>> schedule with preempt disable as console_may_schedule was one
>> and due to which do_cond_resched was one.
> 
> Nice catch. But I think the below patch is the appropriate fix:

Thanks for the change @john, would you be sending this as proper
patch.

-Mukesh
> 
> John Ogness
> 
> -------8<--------
> Subject: [PATCH] printk: Update @console_may_schedule in
>   console_trylock_spinning()
> 
> console_trylock_spinning() may takeover the console lock from a
> scheduable 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
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>   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 scheduable.
> +	 */
> +	console_may_schedule = 0;
> +
>   	return 1;
>   }
>   
> 
> base-commit: e7081d5a9d976b84f61f497316d7c940a4a2e67a