From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932592AbcHIX4Z (ORCPT ); Tue, 9 Aug 2016 19:56:25 -0400 Received: from mail-by2nam03on0063.outbound.protection.outlook.com ([104.47.42.63]:55376 "EHLO NAM03-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750909AbcHIX4V (ORCPT ); Tue, 9 Aug 2016 19:56:21 -0400 Authentication-Results: spf=pass (sender IP is 63.163.107.21) smtp.mailfrom=sandisk.com; cmpxchg.org; dkim=none (message not signed) header.d=none;cmpxchg.org; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: ac160c69-5f3ff70000000bcb-2f-57aa6bbc6751 Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs To: Oleg Nesterov , Bart Van Assche References: <20160803181128.GH6879@twins.programming.kicks-ass.net> <11007730-3fa5-139a-8091-655743894ae8@sandisk.com> <20160803213006.GA11712@redhat.com> <17b65ff9-215f-ab74-9f5f-15dbd308d054@sandisk.com> <20160804140938.GB24652@twins.programming.kicks-ass.net> <16207b90-2e6c-fe23-1b4b-3763e5cf0384@sandisk.com> <20160808102213.GA6879@twins.programming.kicks-ass.net> <4091e252-18d9-1795-de63-9fbc678aa6b1@acm.org> <20160808162038.GA25927@redhat.com> CC: Peter Zijlstra , "mingo@kernel.org" , Andrew Morton , "Johannes Weiner" , Neil Brown , Michael Shaver , "linux-kernel@vger.kernel.org" From: Bart Van Assche Message-ID: <8ca35562-a670-4fe5-fa46-7d1872d90299@sandisk.com> Date: Tue, 9 Aug 2016 16:56:15 -0700 User-Agent: Mozilla/5.0 (X11; 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Say, someone clears > PG_locked without wake_up(). Then SIGKILL sent to the task sleeping in > sys_read() "adds" the necessary wakeup... Hello Oleg, Something that puzzles me is that removing the "else" keyword from abort_exclusive_wait() is sufficient to avoid the hang. If there would be code that clears PG_locked without calling wake_up() this hang probably would also be triggered by workloads that do not wake up lock_page_killable() with a signal. BTW, the WARN_ONCE(!list_empty(&wait->task_list) && waitqueue_active(q), "mode = %#x\n", mode) statement that I added in abort_exclusive_wait() just produced the following call stack: Aug 9 16:16:38 ion-dev-ib-ini kernel: WARNING: CPU: 0 PID: 14767 at kernel/sched/wait.c:284 abort_exclusive_wait+0xe3/0xf0 Aug 9 16:16:38 ion-dev-ib-ini kernel: mode = 0x82 Aug 9 16:16:38 ion-dev-ib-ini kernel: [last unloaded: brd] Aug 9 16:16:38 ion-dev-ib-ini kernel: CPU: 0 PID: 14767 Comm: kpartx Tainted: G W 4.7.0-dbg+ #3 Aug 9 16:16:38 ion-dev-ib-ini kernel: Call Trace: Aug 9 16:16:38 ion-dev-ib-ini kernel: [] dump_stack+0x68/0xa1 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] __warn+0xc6/0xe0 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] warn_slowpath_fmt+0x4a/0x50 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] abort_exclusive_wait+0xe3/0xf0 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] __wait_on_bit_lock+0x61/0xa0 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] __lock_page_killable+0xb9/0xc0 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] generic_file_read_iter+0x1ea/0x770 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] blkdev_read_iter+0x30/0x40 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] __vfs_read+0xbb/0x130 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] vfs_read+0x91/0x130 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] SyS_read+0x44/0xa0 Aug 9 16:16:38 ion-dev-ib-ini kernel: [] entry_SYSCALL_64_fastpath+0x18/0xa8 (gdb) list *(generic_file_read_iter+0x1ea) 0xffffffff8115305a is in do_generic_file_read (mm/filemap.c:1730). 1725 continue; 1726 1727 page_not_up_to_date: 1728 /* Get exclusive access to the page ... */ 1729 error = lock_page_killable(page); 1730 if (unlikely(error)) 1731 goto readpage_error; 1732 1733 page_not_up_to_date_locked: 1734 /* Did it get truncated before we got the lock? */ Apparently the task that hangs is the same task as the one that received the signal (PID 14767; state "D" = TASK_UNINTERRUPTIBLE): [ 3718.134118] sysrq: SysRq : Show Blocked State [ 3718.136234] kpartx D ffff8803c7767838 0 14767 1 0x00000006 [ 3718.136928] Call Trace: [ 3718.137089] [] schedule+0x37/0x90 [ 3718.137142] [] schedule_timeout+0x27f/0x470 [ 3718.137603] [] io_schedule_timeout+0x9f/0x110 [ 3718.137662] [] bit_wait_io+0x16/0x60 [ 3718.137714] [] __wait_on_bit_lock+0x49/0xa0 [ 3718.137764] [] __lock_page+0xb9/0xc0 [ 3718.137865] [] truncate_inode_pages_range+0x3e0/0x760 [ 3718.138175] [] truncate_inode_pages+0x10/0x20 [ 3718.138477] [] kill_bdev+0x30/0x40 [ 3718.138529] [] __blkdev_put+0x71/0x360 [ 3718.138631] [] blkdev_put+0x49/0x170 [ 3718.138681] [] blkdev_close+0x20/0x30 [ 3718.138732] [] __fput+0xe8/0x1f0 [ 3718.138782] [] ____fput+0x9/0x10 [ 3718.138834] [] task_work_run+0x83/0xb0 [ 3718.138886] [] do_exit+0x3ee/0xc40 [ 3718.138987] [] do_group_exit+0x4b/0xc0 [ 3718.139038] [] get_signal+0x2ca/0x940 [ 3718.139142] [] do_signal+0x23/0x660 [ 3718.139247] [] exit_to_usermode_loop+0x73/0xb0 [ 3718.139297] [] syscall_return_slowpath+0xb0/0xc0 [ 3718.139349] [] entry_SYSCALL_64_fastpath+0xa6/0xa8 I'll try to see whether this behavior is reproducible. Bart.