From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 67B7628025C for ; Wed, 28 Sep 2016 03:15:06 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id b130so30686584wmc.2 for ; Wed, 28 Sep 2016 00:15:06 -0700 (PDT) Received: from mail-wm0-f45.google.com (mail-wm0-f45.google.com. [74.125.82.45]) by mx.google.com with ESMTPS id s1si7040127wjm.218.2016.09.28.00.15.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Sep 2016 00:15:04 -0700 (PDT) Received: by mail-wm0-f45.google.com with SMTP id l132so218345043wmf.0 for ; Wed, 28 Sep 2016 00:15:04 -0700 (PDT) Subject: Re: Soft lockup in __slab_free (SLUB) References: <57E8D270.8040802@kyup.com> <20160928053114.GC22706@js1304-P5Q-DELUXE> From: Nikolay Borisov Message-ID: <57EB6DF5.2010503@kyup.com> Date: Wed, 28 Sep 2016 10:15:01 +0300 MIME-Version: 1.0 In-Reply-To: <20160928053114.GC22706@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Christoph Lameter , Linux MM , brouer@redhat.com, "Paul E. McKenney" On 09/28/2016 08:31 AM, Joonsoo Kim wrote: > Hello, > > Ccing Paul, because it looks like RCU problem. > > On Mon, Sep 26, 2016 at 10:46:56AM +0300, Nikolay Borisov wrote: >> Hello, >> >> On 4.4.14 stable kernel I observed the following soft-lockup, however I >> also checked that the code is the same in 4.8-rc so the problem is >> present there as well: >> >> [434575.862377] NMI watchdog: BUG: soft lockup - CPU#13 stuck for 23s! [swapper/13:0] >> [434575.866352] CPU: 13 PID: 0 Comm: swapper/13 Tainted: P O 4.4.14-clouder5 #2 >> [434575.866643] Hardware name: Supermicro X9DRD-iF/LF/X9DRD-iF, BIOS 3.0b 12/05/2013 >> [434575.866932] task: ffff8803714aadc0 ti: ffff8803714c4000 task.ti: ffff8803714c4000 >> [434575.867221] RIP: 0010:[] [] _raw_spin_unlock_irqrestore+0x1c/0x30 >> [434575.867566] RSP: 0018:ffff880373ce3dc0 EFLAGS: 00000203 >> [434575.867736] RAX: ffff88066e0c9a40 RBX: 0000000000000203 RCX: 0000000000000000 >> [434575.868023] RDX: 0000000000000008 RSI: 0000000000000203 RDI: ffff88066e0c9a40 >> [434575.868311] RBP: ffff880373ce3dc8 R08: ffff8803e5c1d118 R09: ffff8803e5c1d538 >> [434575.868609] R10: 0000000000000000 R11: ffffea000f970600 R12: ffff88066e0c9a40 >> [434575.868895] R13: ffffea000f970600 R14: 000000000046cf3b R15: ffff88036f8e3200 >> [434575.869183] FS: 0000000000000000(0000) GS:ffff880373ce0000(0000) knlGS:0000000000000000 >> [434575.869472] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [434575.869643] CR2: ffffffffff600400 CR3: 0000000367201000 CR4: 00000000001406e0 >> [434575.869931] Stack: >> [434575.870095] ffff88066e0c9a40 ffff880373ce3e78 ffffffff8117ea8a ffff880373ce3e08 >> [434575.870567] 000000000046bd03 0000000100170017 ffff8803e5c1d118 ffff8803e5c1d118 >> [434575.871037] 00ff000100000000 0000000000000203 0000000000000000 ffffffff8123d9ac >> [434575.874253] Call Trace: >> [434575.874418] >> [434575.874473] [] __slab_free+0xca/0x290 >> [434575.874806] [] ? ext4_i_callback+0x1c/0x20 >> [434575.874978] [] kmem_cache_free+0x1ea/0x200 >> [434575.875149] [] ext4_i_callback+0x1c/0x20 >> [434575.875325] [] rcu_process_callbacks+0x21b/0x620 >> [434575.875506] [] __do_softirq+0x147/0x310 >> [434575.875680] [] irq_exit+0x5f/0x70 >> [434575.875851] [] smp_apic_timer_interrupt+0x42/0x50 >> [434575.876025] [] apic_timer_interrupt+0x89/0x90 >> [434575.876197] >> [434575.876250] [] ? cpuidle_enter_state+0x141/0x2c0 >> [434575.876583] [] ? cpuidle_enter_state+0x136/0x2c0 >> [434575.876755] [] cpuidle_enter+0x17/0x20 >> [434575.876929] [] cpu_startup_entry+0x2fc/0x360 >> [434575.877105] [] start_secondary+0xf3/0x100 >> >> The ip in __slab_free points to this piece of code (in mm/slub.c): >> >> if (unlikely(n)) { >> spin_unlock_irqrestore(&n->list_lock, flags); >> n = NULL; >> } >> >> I think it's a pure chance that the spin_unlock_restore is being shown in this trace, >> do you think that a cond_resched is needed in this unlikely if clause? Apparently there >> are cases where this loop can take a considerable amount of time. > > I think that __slab_free() doesn't take too long time even if there is > lock contention. And, cond_resched() is valid on softirq context? Now that I think of it - it's not valid since it might sleep and softirq is atomic context. So my suggestion is actually invalid, too bad. > > I think that problem would be caused by too many rcu callback is > executed without scheduling. Paul? I don't think it's an RCU problem per-se since ext4_i_callback is being called from RCU due to the way inodes are being freed. On a slightly different note - on a different physical server, running zfsonlinux I experienced a very similar issue but without being in an RCU context, here what the stacktrace looked there: Call Trace: [] __slab_free+0xca/0x290 [] ? kmem_cache_free+0x1ea/0x200 [] kmem_cache_free+0x1ea/0x200 [] spl_kmem_cache_free+0x147/0x1d0 [spl] [] dnode_destroy+0x1dc/0x230 [zfs] [] dnode_buf_pageout+0x44/0xc0 [zfs] [] taskq_thread+0x291/0x4e0 [spl] [] ? wake_up_q+0x70/0x70 [] ? taskq_thread_spawn+0x50/0x50 [spl] [] kthread+0xef/0x110 [] ? kthread_park+0x60/0x60 [] ret_from_fork+0x3f/0x70 [] ? kthread_park+0x60/0x60 It's hard to believe this is a coincidence. I've inspected the callpaths in the taskq_thread/dnode_buf_pageout/dnode_destroy and there doesn't seem to be a loop apart from the one in __slab_free. [SNIP] -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org