From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2ED34B660 for ; Fri, 19 Jul 2024 14:55:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721400914; cv=none; b=IdfXLLTl6fHK5JOg0jMXewIlNB38b+PjH3ynepFu5n76Zy76hSuX0NwZNka8u28gvO/feRDUqyksenDjFY+YblsO5Cx+7DwD0QXykD6I0a1LVpuIpEIlZeCf2MSu/0X7VA2FXkeFcQn2DcxZSugLKjfevr7mtc8iXXorlxrZyQw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721400914; c=relaxed/simple; bh=PFzUXLr2/yALo990FkQ2QDF5O2PzYhQJEs4gMrZISZ0=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=DDe1U4OqiH5wivQGaeJ+qBUEOU0Egv5OfSMTM6HlY6pGSlm8tkiesdWPCU8Iu8CU8bOWmuwM5XljYhY5T3E5X4KB781LhdfZs5EyIuNt8l5UwyiGRrBin+zbpEerTG4TrpZWa64n5GEsXbmZAx7mNbnfi5JbZjTV22XAz520gZ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=c3RuwRiU; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=MfwRj4s4; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="c3RuwRiU"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="MfwRj4s4" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1721400911; h=from:from:reply-to:subject:subject: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=Aw8kciyHPzVi8pszzCEIhgoe0SL2OLBRAVuwP3WpnxI=; b=c3RuwRiU/lbje9aKFcT9kFa1aX+wl28Xx/TaX8zYCMUL/Dd0OGA5fHnxCE/Oz+R//94N/Y 83NM0SYiG5tklkEcnbbi5CqWyEScGqEIKxtaN7TOhFL5xNWu3XDgcwTQwrZO7a2mRFF9Cy CLWLGSbDubgYddsDHB4z9/jPOY1f+1Xdwinv/fEiEkNqh5mKvXapSLllTaqoEYGbavZC/Z H3YhglzYWFakgrx4GMbfsuW11Z7wOdknuUuPZ4urZZLXNQLW9NpZJAU+1XmHXfLrjB/dqV rTqD95hAA4MRFOBKDEB9uxGpGpdiFVd5t6BvSxZQE4XjBqtqHgfkwYwhexslAQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1721400911; h=from:from:reply-to:subject:subject: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=Aw8kciyHPzVi8pszzCEIhgoe0SL2OLBRAVuwP3WpnxI=; b=MfwRj4s4tfEahXECyIqs3XKERY6akf/ihvGhzUBmutWB+tu5XYkS579oBwB23JTbzhohp4 Z5UJtmMLWK16QTBg== To: Andrew Halaney Cc: Steven Rostedt , pmladek@suse.com, senozhatsky@chromium.org, debarbos@redhat.com, williams@redhat.com, jlelli@redhat.com, linux-rt-users@vger.kernel.org Subject: Re: [BUG] printk/nbcon can use RCU illegally prior to CPU online In-Reply-To: References: <5x4nejpojrtny37k7l6loewqwuaituq77zc3tkkojvawcuvmml@thwg65fdb3vn> <20240718115704.0cd768bc@rorschach.local.home> <436jncgrfxwcizjw5gxw3yar5ybo62zdctout6sti6gamwtnlw@gqrmo5ine6d2> <87cyn9lssy.fsf@jogness.linutronix.de> Date: Fri, 19 Jul 2024 17:01:10 +0206 Message-ID: <874j8ll9dd.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On 2024-07-19, Andrew Halaney wrote: >> Your thinking is not naive. It is correct (for PREEMPT_RT). printk() >> stores messages locklessly into its ringbuffer and must work in all >> cases (including NMI and scheduler). And AFAIK it does. >> >> However, printk() is also responsible for reliably triggering or >> performing console printing. This separate responsibility is tricky. For >> PREEMPT_RT the problem is supposed to be solved. Obviously it still has >> some issues, so thank you for the report. >> >> For PREEMPT_RT, if you can put a printk() anywhere after the Linux >> banner and cause a problem, the printk-folks need to know about it. > > Just to be sure I'm following correctly, when you say PREEMPT_RT above, > are you meaning "the printk/nbcon/console solution in PREEMPT (independent of > the current CONFIG_PREEMPT* setting)"? Or do you mean that + CONFIG_PREEMPT_RT? First, the _complete_ printk/nbcon/console solution must be present in the kernel (most likely by simply applying the PREEMPT_RT patchset). Then, either 1. Enabling CONFIG_PREEMPT_RT or 2. Enabling some other preemption model but only using nbcon consoles (which currently is only the 8250 uart driver) For !CONFIG_PREEMPT_RT using legacy consoles the non-interference/reliability properties of the console printing is not changed from current mainline. This is on purpose. John