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 3665E187FE8; Fri, 18 Oct 2024 07:14:22 +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=1729235664; cv=none; b=bi6cNk6Hq1Ec3EhrW8qJ8PS+hRD3EDUIf4f8oBLxSZXnw+LNoxvmw1oBCuuZCyhMVvgdU+NamG5rs8p4onezgAutdZb2ZBuFynSC7dpfRss6DiJqKhPPPg8mIxsnXqkjAFcQW24YA9J5Sg8BMxuk9DxKhSp75XVpPOnkgRZRIBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729235664; c=relaxed/simple; bh=xCAUbdnqvgNV/V6oAIWT+m3/O2zlkGatZfSoz/Xnnhw=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=mOMkwAUKf9ljlq5La0wL7KjMli7DIvcD0+RrhPDBgllyRe+JjLdW3uxQvTXKp5DxXJDiC0pufkqsOKnrDUOcJRIWINHdD9tZvMPgQwOUBFUa3emX5cLXOoReZmusUeHMb1wDmLVDak/mp2q8VDl9YUwbK75Z5D0qwVgdGWAJNSk= 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=DDelpabA; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=xMTGE46Q; 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="DDelpabA"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="xMTGE46Q" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1729235660; 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=+Z7JsCpFB189JSy0DnbwO4yluBbFguCW7D+UFmq9dhg=; b=DDelpabAhrUyYlZ+yz56Bu79pNAk8o0gShQvPSD3iTU8mVHPXnzUfDGayY68bkEu+SGdkQ et9yQKTQU23jITDkDcCs1JTsp4br0TWd3hVK0HTbU+ioQnkjnckWxpvrfXw7i/I5bXwvce Haf/XfWcTY+4HAr1jYQa1IQ0rTdzqdcFgrcejXQgufKlM18Ir52WVGmrrvdMgVt3McQs4n j8914B9WSK1oa+t9/KyYEq9QSPr51ACF3TpR+vde6juplG91qFQiJve60TL2giEu0Gmwxe LsGSMvvbjv9qyo+wIThRcZlFBUOVc6l9bFM0CPcFFiezR25G6Pt5d78JMNXu6w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1729235660; 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=+Z7JsCpFB189JSy0DnbwO4yluBbFguCW7D+UFmq9dhg=; b=xMTGE46Qxq+mCNBb8Hto5m3Hf/zdqhBW1SlINfm80YgGairf7jg9J4MD+6qSPmXx+Ohf+/ 7NMIrI3HPl5upzAQ== To: Petr Mladek Cc: Marcos Paulo de Souza , Steven Rostedt , Sergey Senozhatsky , Greg Kroah-Hartman , Jiri Slaby , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: Re: [PATCH 1/2] printk: Introduce LOUD_CON flag In-Reply-To: References: <20241016-printk-loud-con-v1-0-065e4dad6632@suse.com> <20241016-printk-loud-con-v1-1-065e4dad6632@suse.com> <84plnz29zv.fsf@jogness.linutronix.de> Date: Fri, 18 Oct 2024 09:20:19 +0206 Message-ID: <847ca5rigk.fsf@jogness.linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On 2024-10-17, Petr Mladek wrote: > # echo h >/proc/sysrq-trigger > > produced: > > [ 53.669907] BUG: assuming non migratable context at kernel/printk/printk_safe.c:23 > [ 53.669920] in_atomic(): 0, irqs_disabled(): 0, migration_disabled() 0 pid: 1637, name: bash > [ 53.669931] 2 locks held by bash/1637: > [ 53.669936] #0: ffff8ae680a384a8 (sb_writers#4){.+.+}-{0:0}, at: ksys_write+0x6e/0xf0 > [ 53.669968] #1: ffffffff83f226e0 (rcu_read_lock){....}-{1:3}, at: __handle_sysrq+0x3d/0x120 > [ 53.670002] CPU: 2 UID: 0 PID: 1637 Comm: bash Not tainted 6.12.0-rc3-default+ #67 > [ 53.670011] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-2-gc13ff2cd-prebuilt.qemu.org 04/01/2014 > [ 53.670020] Call Trace: > [ 53.670026] > [ 53.670045] dump_stack_lvl+0x6c/0xa0 > [ 53.670064] __cant_migrate.cold+0x7c/0x89 > [ 53.670080] printk_loud_console_enter+0x15/0x30 > [ 53.670088] __handle_sysrq+0x60/0x120 > [ 53.670104] write_sysrq_trigger+0x6a/0xa0 > [ 53.670120] proc_reg_write+0x5f/0xb0 > [ 53.670132] vfs_write+0xf9/0x540 > [ 53.670147] ? __lock_release.isra.0+0x1a6/0x2c0 > [ 53.670172] ? do_user_addr_fault+0x38c/0x720 > [ 53.670197] ksys_write+0x6e/0xf0 > [ 53.670220] do_syscall_64+0x79/0x190 > [ 53.670238] entry_SYSCALL_64_after_hwframe+0x76/0x7e > > IMHO, the best solution would be to call migrate_disable()/enable() > in printk_loud_console_enter()/exit(). That will not work because migrate_enable() can only be called from can_sleep context. Instead, the migrate_disable()/enable() should be at the few (one?) call sites where printk_loud_console_enter()/exit() is used from task context. This is also how printk_deferred_enter()/exit() works, relying on the caller to disable migration if necessary. John