From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEF0FEE6447 for ; Fri, 15 Sep 2023 08:38:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232915AbjIOIiM (ORCPT ); Fri, 15 Sep 2023 04:38:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231949AbjIOIiL (ORCPT ); Fri, 15 Sep 2023 04:38:11 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C8D9F1FD0 for ; Fri, 15 Sep 2023 01:38:03 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 759F92186F; Fri, 15 Sep 2023 08:38:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1694767082; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=xfgyyzazrOp9lV1wfwFfoCZhiUNB4T4EERql1ERZJ8A=; b=gI0wlMXwJJUUmgLw519e+ocIuJsOWQCaE+nOhNYG1+onzCkWe8UMbt4M9IpQ2usOGPCwfY SFP3ZiFVsYZJJ4cp99fQFhLlubZiH4jWPZodRUQLAm+Q1em9UjHpzaMRniUmFBcJScVFvO m6tUnOxjKGJ7hsZE2lNSqJcnAMFEIf8= Received: from suse.cz (pmladek.tcp.ovpn2.prg.suse.de [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 2201E2C142; Fri, 15 Sep 2023 08:38:02 +0000 (UTC) Date: Fri, 15 Sep 2023 10:38:01 +0200 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Greg Kroah-Hartman Subject: Re: [PATCH printk v4 8/8] printk: nbcon: Allow drivers to mark unsafe regions and check state Message-ID: References: <20230908185008.468566-1-john.ogness@linutronix.de> <20230908185008.468566-9-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230908185008.468566-9-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2023-09-08 20:56:08, John Ogness wrote: > From: Thomas Gleixner > > For the write_atomic callback, the console driver may have unsafe > regions that need to be appropriately marked. Provide functions > that accept the nbcon_write_context struct to allow for the driver > to enter and exit unsafe regions. > > Also provide a function for drivers to check if they are still the > owner of the console. > > diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c > index e2c274f4142e..04fac73c6e96 100644 > --- a/kernel/printk/nbcon.c > +++ b/kernel/printk/nbcon.c > @@ -660,6 +660,32 @@ static bool nbcon_context_can_proceed(struct nbcon_context *ctxt, struct nbcon_s > return false; > } > > +/** > + * nbcon_can_proceed - Check whether ownership can proceed > + * @wctxt: The write context that was handed to the write function > + * > + * Return: True if this context still owns the console. False if > + * ownership was handed over or taken. > + * > + * Must be invoked at appropriate safe places in the driver. This is a bit vague. I guess that enter_unsafe()/exit_unsafe() will be used most of the time. The guestion is if this need to be called in another locations explicitely. I would write something similar as I suggested for nbcon_context_can_proceed(): * It is used in nbcon_enter_unsafe() to make sure that it still owns the lock. * Also it is used in nbcon_exit_unsafe() to eventually free the lock * for a higher priority context which asked for the friendly handover. * * It can be called inside an unsafe section when the console is just * temporary in safe state instead of exiting and entering the unsafe * state. * * Also it can be called in the safe context before doing an expensive * safe operation. It does not make sense to do the operation when * a higher priority context took the lock. > + * > + * When this function returns false then the calling context no longer owns > + * the console and is no longer allowed to go forward. In this case it must > + * back out immediately and carefully. The buffer content is also no longer > + * trusted since it no longer belongs to the calling context. > + */ > +bool nbcon_can_proceed(struct nbcon_write_context *wctxt) > +{ > + struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt); > + struct console *con = ctxt->console; > + struct nbcon_state cur; > + > + nbcon_state_read(con, &cur); > + > + return nbcon_context_can_proceed(ctxt, &cur); > +} > +EXPORT_SYMBOL_GPL(nbcon_can_proceed); > + With the updated comment: Reviewed-by: Petr Mladek Best Regards, Petr