From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752011AbdF3LsF (ORCPT ); Fri, 30 Jun 2017 07:48:05 -0400 Received: from mail-db5eur01on0092.outbound.protection.outlook.com ([104.47.2.92]:11012 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751638AbdF3Lre (ORCPT ); Fri, 30 Jun 2017 07:47:34 -0400 Authentication-Results: de.ibm.com; dkim=none (message not signed) header.d=none;de.ibm.com; dmarc=none action=none header.from=virtuozzo.com; Subject: Re: [PATCH] mm/memory-hotplug: Switch locking to a percpu rwsem To: Thomas Gleixner , Michal Hocko Cc: LKML , "linux-mm@kvack.org" , Andrew Morton , Vlastimil Babka , Vladimir Davydov , Heiko Carstens References: <20170630092747.GD22917@dhcp22.suse.cz> From: Andrey Ryabinin Message-ID: <3f2395c6-bbe0-23c1-fe06-d17ffbf619c3@virtuozzo.com> Date: Fri, 30 Jun 2017 14:49:24 +0300 User-Agent: Mozilla/5.0 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1;HE1PR0801MB2729;7: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 X-Microsoft-Exchange-Diagnostics: 1;HE1PR0801MB2729;20:UpXW2l11lSM70c6nu4jFGF3XnN1jPpm1/8MlGLU84oEiYDN9Qzcon1Ct6J29xB3oOWiWrcbGf+r8fVApxuupBQdT21RNpUlzKV7NDGXYOZ70Pm3PWkH8+3pdLWgxt84xdaM5UrD/3Mmi0t/MhJl7OomdsEnuqEKLQpqneLiOFc4= X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jun 2017 11:47:24.3997 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0801MB2729 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/30/2017 01:15 PM, Thomas Gleixner wrote: > On Fri, 30 Jun 2017, Michal Hocko wrote: >> So I like this simplification a lot! Even if we can get rid of the >> stop_machine eventually this patch would be an improvement. A short >> comment on why the per-cpu semaphore over the regular one is better >> would be nice. > > Yes, will add one. > > The main point is that the current locking construct is evading lockdep due > to the ability to support recursive locking, which I did not observe so > far. > Like this? [ 131.022567] ============================================ [ 131.023034] WARNING: possible recursive locking detected [ 131.023034] 4.12.0-rc7-next-20170630 #10 Not tainted [ 131.023034] -------------------------------------------- [ 131.023034] bash/2266 is trying to acquire lock: [ 131.023034] (cpu_hotplug_lock.rw_sem){++++++}, at: [] lru_add_drain_all+0x42/0x190 [ 131.023034] but task is already holding lock: [ 131.023034] (cpu_hotplug_lock.rw_sem){++++++}, at: [] mem_hotplug_begin+0x9/0x20 [ 131.023034] other info that might help us debug this: [ 131.023034] Possible unsafe locking scenario: [ 131.023034] CPU0 [ 131.023034] ---- [ 131.023034] lock(cpu_hotplug_lock.rw_sem); [ 131.023034] lock(cpu_hotplug_lock.rw_sem); [ 131.023034] *** DEADLOCK *** [ 131.023034] May be due to missing lock nesting notation [ 131.023034] 8 locks held by bash/2266: [ 131.023034] #0: (sb_writers#8){.+.+.+}, at: [] vfs_write+0x1a8/0x1d0 [ 131.023034] #1: (&of->mutex){+.+.+.}, at: [] kernfs_fop_write+0xfc/0x1b0 [ 131.023034] #2: (s_active#48){.+.+.+}, at: [] kernfs_fop_write+0x104/0x1b0 [ 131.023034] #3: (device_hotplug_lock){+.+.+.}, at: [] lock_device_hotplug_sysfs+0x10/0x40 [ 131.023034] #4: (cpu_hotplug_lock.rw_sem){++++++}, at: [] mem_hotplug_begin+0x9/0x20 [ 131.023034] #5: (mem_hotplug_lock.rw_sem){++++++}, at: [] percpu_down_write+0x21/0x110 [ 131.023034] #6: (&dev->mutex){......}, at: [] device_offline+0x45/0xb0 [ 131.023034] #7: (lock#3){+.+...}, at: [] lru_add_drain_all+0x3d/0x190 [ 131.023034] stack backtrace: [ 131.023034] CPU: 0 PID: 2266 Comm: bash Not tainted 4.12.0-rc7-next-20170630 #10 [ 131.023034] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014 [ 131.023034] Call Trace: [ 131.023034] dump_stack+0x85/0xc7 [ 131.023034] __lock_acquire+0x1747/0x17a0 [ 131.023034] ? lru_add_drain_all+0x3d/0x190 [ 131.023034] ? __mutex_lock+0x218/0x940 [ 131.023034] ? trace_hardirqs_on+0xd/0x10 [ 131.023034] lock_acquire+0x103/0x200 [ 131.023034] ? lock_acquire+0x103/0x200 [ 131.023034] ? lru_add_drain_all+0x42/0x190 [ 131.023034] cpus_read_lock+0x3d/0x80 [ 131.023034] ? lru_add_drain_all+0x42/0x190 [ 131.023034] lru_add_drain_all+0x42/0x190 [ 131.023034] __offline_pages.constprop.25+0x5de/0x870 [ 131.023034] offline_pages+0xc/0x10 [ 131.023034] memory_subsys_offline+0x43/0x70 [ 131.023034] device_offline+0x83/0xb0 [ 131.023034] store_mem_state+0xdb/0xe0 [ 131.023034] dev_attr_store+0x13/0x20 [ 131.023034] sysfs_kf_write+0x40/0x50 [ 131.023034] kernfs_fop_write+0x130/0x1b0 [ 131.023034] __vfs_write+0x23/0x130 [ 131.023034] ? rcu_read_lock_sched_held+0x6d/0x80 [ 131.023034] ? rcu_sync_lockdep_assert+0x2a/0x50 [ 131.023034] ? __sb_start_write+0xd4/0x1c0 [ 131.023034] ? vfs_write+0x1a8/0x1d0 [ 131.023034] vfs_write+0xc8/0x1d0 [ 131.023034] SyS_write+0x44/0xa0 [ 131.023034] entry_SYSCALL_64_fastpath+0x1f/0xbe [ 131.023034] RIP: 0033:0x7fb6b54ac310 [ 131.023034] RSP: 002b:00007ffcb7b123e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 131.023034] RAX: ffffffffffffffda RBX: 00007fb6b5767640 RCX: 00007fb6b54ac310 [ 131.023034] RDX: 0000000000000008 RSI: 00007fb6b5e2d000 RDI: 0000000000000001 [ 131.023034] RBP: 0000000000000007 R08: 00007fb6b57687a0 R09: 00007fb6b5e23700 [ 131.023034] R10: 0000000000000098 R11: 0000000000000246 R12: 0000000000000007 [ 131.023034] R13: 000000000173e9f0 R14: 0000000000000000 R15: 0000000000491569