From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=193.142.43.55 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793288576; b=b64kPyXhVL7XgfXJCQDTGYAGj2qFEcOoCZb9JNfIaNPXYCvfNxN00XnihWhlRzn3tT2+ J4fbMsasTfNEMmaq0dbsYRkai865tqJ66vFd8CgjyynBfqeP1Bnxiuu4KCMvL1aSOb7CB OmimTYrP6TDUj8AW8GjS6twOv+y7zA6Ox8iotERYTNMnLV/1JspoECaaRmmnr0iMolVgY iZNIHtuFrLPK6dnh3itROH3IXfL0l/QtfHWBR92YwSSPwslfUGFTyZ18fqotjwKSMgNUY S8/dgMhzYOnDgVyCTTqL4ZB+U3rx8nIIvUw+ToSG63bnW6XxCStsmkL+pZcVY6QBhMw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793288576; h=DMARC-Filter:From:DKIM-Signature:DKIM-Signature:To:Cc:Subject: In-Reply-To:References:Date:Message-ID:MIME-Version:Content-Type; bh=L5D86BXNnNkH5tFHqH3VjPCbsL8RXaLh8X9LuOfrSFk=; b=B7eHRT3rle0qmic/tkYeHrsJkHzQG+1yXF8ZSX5JtboSMCdtjtn35jVUdCH0r/h9EWAN /nCvfCcIaIGZymUHWkAPN1nnS5Z9PcGy6+J15UEOW85mfCDC2R6EICqzK3UBLaiDHPBnJ K/vwmWbyaW27g/i5rC2d6gy0JpgNTuFjduERGXg+r465NtQ2Yt3G8cR7K7Hnv+dPVCxP5 KfGfT4JnfebY+T/mwVDIc2Y6aWJsqnvYtVMNjW7nVhhmj+1x1cdaFfsHrObGCmzUZd+xw snUAmVObXzDyhYVz5VPsWAeEMzv/07obc8AOI956bMpUxXbXl88+TlxN9N9dAfWM4tQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b="1mI/KKbJ"; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=9wAXUyVG; arc=none smtp.remote-ip=193.142.43.55 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F3C06606A31A for ; Thu, 29 Oct 2026 15:42:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org F3C06606A31A 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, unprotected) header.d=linutronix.de header.i=@linutronix.de header.a=rsa-sha256 header.s=2020 header.b=1mI/KKbJ; dkim=pass header.d=linutronix.de header.i=@linutronix.de header.a=ed25519-sha256 header.s=2020e header.b=9wAXUyVG From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1793288573; 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=L5D86BXNnNkH5tFHqH3VjPCbsL8RXaLh8X9LuOfrSFk=; b=1mI/KKbJifBl0xlBKIAJQI5uhaZN8dMQjYjmpybz0Hs+oTnviJ/TbplPRsxaQPtNHKYWjn Dr2ntFgMmAwHvKY9YHBIvrSX7RAPHF9Jup7Q/M7wDba5u4N8E1t2+4R1o1/wkWbjlnRI9l NiRLsga938a3UTCo62NJ7YUZ72Qm69KLMGOYqrYNudGadaYU+ESXVsFaaOuq/rxLGu96rn sKbt7UPliR6n8/rfOTbpegPn62L+3sgK/InfSW160zm63yE9ywTOAROxNAX54RvqZn8EHr sH0RrqKYclePkmERALeKF3o3TnMv62pTJeySd8QVZSdxRTedFBlg78vh+rn85g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1793288573; 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=L5D86BXNnNkH5tFHqH3VjPCbsL8RXaLh8X9LuOfrSFk=; b=9wAXUyVGxrwz9T1YeevfYK4dIfmJb0V0hUFOvHAOoIkphgQV4b7u6m6Gzy3VaQ7oc6aAMd RSFkcorc/oIJIVCA== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Derek Barbosa , printk@lists.linux.dev, linux-kernel@vger.kernel.org, Sashiko Subject: Re: [PATCH printk] printk: Avoid multiple unregistration in unregister_console_locked() In-Reply-To: <20261029152454.638952-1-john.ogness@linutronix.de> References: <20261029152454.638952-1-john.ogness@linutronix.de> Date: Thu, 29 Oct 2026 16:48:53 +0106 Message-ID: <87y0bgwm0y.fsf@jogness.linutronix.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain On 2026-10-29, Sashiko wrote: >> @@ -4471,6 +4493,9 @@ static int __init printk_late_init(void) >> } >> >> unregister_console_locked(con); >> + >> + /* Changed console list, may require printer threads to start/stop. */ >> + printk_kthreads_check_locked(); >> } > > Should printk_kthreads_check_locked() be called after the > hlist_for_each_entry_safe(con, tmp, &console_list, node) loop in > printk_late_init() rather than inside the loop body? > > In kernel/printk/printk.c:printk_late_init(): > > hlist_for_each_entry_safe(con, tmp, &console_list, node) { > if (!(con->flags & CON_BOOT)) > continue; > ... > unregister_console_locked(con); > > /* Changed console list, may require printer threads to start/stop. */ > printk_kthreads_check_locked(); > } > console_list_unlock(); > > Because printk_kthreads_check_locked() is placed inside the loop, > unregistering the last boot console sets have_boot_console to false and > immediately attempts to start printer kthreads while the loop is still > iterating over console_list. > > If kthread creation in legacy_kthread_create() or nbcon_kthread_create() > fails for the console stored in tmp, printk_kthreads_check_locked() calls > unregister_console_locked() on that console, removing it with > hlist_del_init_rcu(), freeing nbcon resources, and invoking console->exit(). > On the next iteration of printk_late_init(), con is set to tmp, accessing the > already-unregistered console and terminating the walk early because > hlist_del_init_rcu() cleared tmp->next. Geez, sorry. Obviously printk_kthreads_check_locked() needs to be outside of the hlist_for_each_entry_safe(console_list) loop. That was the whole point of the series! I will wait a day for v2 in case there is any feedback regarding my comments (or lack thereof). John