From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754071AbcLIO2Z (ORCPT ); Fri, 9 Dec 2016 09:28:25 -0500 Received: from mail-wj0-f193.google.com ([209.85.210.193]:34163 "EHLO mail-wj0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754018AbcLIO2X (ORCPT ); Fri, 9 Dec 2016 09:28:23 -0500 Date: Fri, 9 Dec 2016 15:28:20 +0100 From: Michal Hocko To: Andy Lutomirski Cc: LKML Subject: BUG: using smp_processor_id() in preemptible [00000000] during put_task_stack Message-ID: <20161209142820.GA4334@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andy, I am hitting the following [ 570.715345] BUG: using smp_processor_id() in preemptible [00000000] code: umount/6193 [ 570.716880] caller is debug_smp_processor_id+0x17/0x19 [ 570.717876] CPU: 2 PID: 6193 Comm: umount Tainted: G W 4.9.0-rc8-nofstest4-next-20161209-00012-g0db618dfb2cf #1017 [ 570.720162] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014 [ 570.720862] Call Trace: [ 570.720862] dump_stack+0x68/0x92 [ 570.720862] check_preemption_disabled+0xce/0xe0 [ 570.720862] debug_smp_processor_id+0x17/0x19 [ 570.720862] vfree_atomic+0x2f/0x65 [ 570.720862] put_task_stack+0xd0/0x13c [ 570.720862] kthread_stop+0x108/0x29a [ 570.720862] destroy_workqueue+0x167/0x1fb [ 570.720862] ext4_put_super+0x44/0x2fa [ 570.720862] generic_shutdown_super+0x6a/0xeb [ 570.720862] kill_block_super+0x27/0x67 [ 570.720862] deactivate_locked_super+0x30/0x68 [ 570.720862] deactivate_super+0x3e/0x41 [ 570.720862] cleanup_mnt+0x58/0x76 [ 570.720862] __cleanup_mnt+0x12/0x14 [ 570.720862] task_work_run+0x77/0xa0 [ 570.720862] exit_to_usermode_loop+0x67/0x92 [ 570.720862] do_syscall_64+0x16c/0x197 [ 570.720862] entry_SYSCALL64_slow_path+0x25/0x25 it seems that vfre_atomic doesn't like it has preemption enabled in __vfree_deferred which calls this_cpu_ptr. I haven't studied the code deeply but I guess what we want is to put vfree_atomic into the atomic context. Something like the following or at least disable preemption around vfree_atomic. Or maybe I am completely missing what the above warning tries to tell... diff --git a/kernel/fork.c b/kernel/fork.c index 8f63bf912195..1c69561eec55 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -227,9 +227,9 @@ static inline void free_thread_stack(struct task_struct *tsk) local_irq_restore(flags); return; } + vfree_atomic(tsk->stack); local_irq_restore(flags); - vfree_atomic(tsk->stack); return; } #endif -- Michal Hocko SUSE Labs