linux-kernel - Re: [PATCH 5.15-rt] printk: ignore consoles without write() callback

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Message-ID: <20250423-singing-bat-60c6f6@krishanthj>
Date: Wed, 23 Apr 2025 15:40:17 +0530
From: Krishanth Jagaduri <krishanth.jagaduri@...y.com>
To: John Ogness <john.ogness@...utronix.de>,
        Joseph Salisbury <joseph.salisbury@...cle.com>
Cc: Clark Williams <williams@...hat.com>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Michael Thalmeier <michael.thalmeier@...e.at>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        Kento.A.Kobayashi@...y.com, Daniel.Palmer@...y.com
Subject: Re: [PATCH 5.15-rt] printk: ignore consoles without write() callback

On Thu, Feb 16, 2023 at 11:45:58AM +0106, John Ogness wrote:
> The ttynull driver does not provide an implementation for the write()
> callback. This leads to a NULL pointer dereference in the related
> printing kthread, which assumes it can call that callback.
> 
> Do not create kthreads for consoles that do not implement the write()
> callback. Also, for pr_flush(), ignore consoles that do not implement
> write() or write_atomic() since there is no way those consoles can
> flush their output.
> 
> ---
>  This is only a problem for the PREEMPT_RT tree. Mainline does not have
>  this problem.

Sorry for resurrecting this old thread but we actually want this patch
in 5.15-rt.

I am not sure why this was not applied to 5.15-rt yet since it is already
applied to 5.10-rt.

Could you please consider to pick this for 5.15-rt?

Best regards,
Krishanth