linux-kernel - Re: [PATCH v8 06/21] printk: nbcon: Synchronise console unregistration against atomic flushers

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Message-ID: <aTmN9fUiJt5gm6Vq@pathway>
Date: Wed, 10 Dec 2025 16:12:53 +0100
From: Petr Mladek <pmladek@...e.com>
To: Chris Down <chris@...isdown.name>
Cc: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Tony Lindgren <tony.lindgren@...ux.intel.com>, kernel-team@...com
Subject: Re: [PATCH v8 06/21] printk: nbcon: Synchronise console
 unregistration against atomic flushers

On Fri 2025-11-28 03:43:32, Chris Down wrote:
> The nbcon atomic flush path in __nbcon_atomic_flush_pending_con() calls
> nbcon_emit_next_record(), which uses console_srcu_read_flags() to read
> the console flags. console_srcu_read_flags() expects to be called under
> console_srcu_read_lock(), but the atomic flush path does not hold this
> lock.

__nbcon_atomic_flush_pending_con() seems to be called in the following
code paths:

  + __nbcon_atomic_flush_pending()
    + nbcon_atomic_flush_pending_con()
      + __nbcon_atomic_flush_pending_con()

 + nbcon_device_release()
   + __nbcon_atomic_flush_pending_con()

 + kdb_msg_write()		# new in 6.19-rc1
   + nbcon_kdb_release()
     + __nbcon_atomic_flush_pending_con()

And all three callers take console_srcu_read_lock() because
they need it for other reasons. So, we should be on the safe
side and do not need this change.

Or do I miss some code path, please?

Best Regards,
Petr