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Date: Wed, 24 Jun 2015 18:15:25 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com,
linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
riel@...hat.com, viro@...IV.linux.org.uk,
torvalds@...ux-foundation.org
Subject: Re: [RFC][PATCH 09/13] hotplug: Replace hotplug lock with
percpu-rwsem
On Wed, Jun 24, 2015 at 05:12:12PM +0200, Oleg Nesterov wrote:
> On 06/24, Peter Zijlstra wrote:
> > I'm confused.. why isn't the read-in-read recursion good enough?
>
> Because the code above can actually deadlock if 2 CPU's do this at
> the same time?
Hmm yes.. this makes the hotplug locking worse than I feared it was, but
alas.
FYI, the actual splat.
---
[ 7.399737] ======================================================
[ 7.406640] [ INFO: possible circular locking dependency detected ]
[ 7.413643] 4.1.0-02756-ge3d06bd-dirty #185 Not tainted
[ 7.419481] -------------------------------------------------------
[ 7.426483] kworker/0:1/215 is trying to acquire lock:
[ 7.432221] (&cpu_hotplug.rwsem){++++++}, at: [<ffffffff810ebd63>] apply_workqueue_attrs+0x183/0x4b0
[ 7.442564]
[ 7.442564] but task is already holding lock:
[ 7.449079] (&item->mutex){+.+.+.}, at: [<ffffffff815c4dc3>] drm_global_item_ref+0x33/0xe0
[ 7.458455]
[ 7.458455] which lock already depends on the new lock.
[ 7.458455]
[ 7.467591]
[ 7.467591] the existing dependency chain (in reverse order) is:
[ 7.475949]
-> #3 (&item->mutex){+.+.+.}:
[ 7.480662] [<ffffffff811232b1>] lock_acquire+0xd1/0x290
[ 7.487280] [<ffffffff818ea777>] mutex_lock_nested+0x47/0x3c0
[ 7.494390] [<ffffffff815c4dc3>] drm_global_item_ref+0x33/0xe0
[ 7.501596] [<ffffffff815dcd90>] mgag200_mm_init+0x50/0x1c0
[ 7.508514] [<ffffffff815d757f>] mgag200_driver_load+0x30f/0x500
[ 7.515916] [<ffffffff815b1491>] drm_dev_register+0xb1/0x100
[ 7.522922] [<ffffffff815b428d>] drm_get_pci_dev+0x8d/0x1e0
[ 7.529840] [<ffffffff815dbd3f>] mga_pci_probe+0x9f/0xc0
[ 7.536463] [<ffffffff814bde92>] local_pci_probe+0x42/0xa0
[ 7.543283] [<ffffffff810e54e8>] work_for_cpu_fn+0x18/0x30
[ 7.550106] [<ffffffff810e9d57>] process_one_work+0x1e7/0x7e0
[ 7.557214] [<ffffffff810ea518>] worker_thread+0x1c8/0x460
[ 7.564029] [<ffffffff810f05b6>] kthread+0xf6/0x110
[ 7.570166] [<ffffffff818eefdf>] ret_from_fork+0x3f/0x70
[ 7.576792]
-> #2 (drm_global_mutex){+.+.+.}:
[ 7.581891] [<ffffffff811232b1>] lock_acquire+0xd1/0x290
[ 7.588514] [<ffffffff818ea777>] mutex_lock_nested+0x47/0x3c0
[ 7.595622] [<ffffffff815b1406>] drm_dev_register+0x26/0x100
[ 7.602632] [<ffffffff815b428d>] drm_get_pci_dev+0x8d/0x1e0
[ 7.609547] [<ffffffff815dbd3f>] mga_pci_probe+0x9f/0xc0
[ 7.616170] [<ffffffff814bde92>] local_pci_probe+0x42/0xa0
[ 7.622987] [<ffffffff810e54e8>] work_for_cpu_fn+0x18/0x30
[ 7.629806] [<ffffffff810e9d57>] process_one_work+0x1e7/0x7e0
[ 7.636913] [<ffffffff810ea518>] worker_thread+0x1c8/0x460
[ 7.643727] [<ffffffff810f05b6>] kthread+0xf6/0x110
[ 7.649866] [<ffffffff818eefdf>] ret_from_fork+0x3f/0x70
[ 7.656490]
-> #1 ((&wfc.work)){+.+.+.}:
[ 7.661104] [<ffffffff811232b1>] lock_acquire+0xd1/0x290
[ 7.667727] [<ffffffff810e737d>] flush_work+0x3d/0x260
[ 7.674155] [<ffffffff810e9822>] work_on_cpu+0x82/0x90
[ 7.680584] [<ffffffff814bf2a2>] pci_device_probe+0x112/0x120
[ 7.687692] [<ffffffff815e685f>] driver_probe_device+0x17f/0x2e0
[ 7.695094] [<ffffffff815e6a94>] __driver_attach+0x94/0xa0
[ 7.701910] [<ffffffff815e4786>] bus_for_each_dev+0x66/0xa0
[ 7.708824] [<ffffffff815e626e>] driver_attach+0x1e/0x20
[ 7.715447] [<ffffffff815e5ed8>] bus_add_driver+0x168/0x210
[ 7.722361] [<ffffffff815e7880>] driver_register+0x60/0xe0
[ 7.729180] [<ffffffff814bd754>] __pci_register_driver+0x64/0x70
[ 7.736580] [<ffffffff81f9a10d>] pcie_portdrv_init+0x66/0x79
[ 7.743593] [<ffffffff810002c8>] do_one_initcall+0x88/0x1c0
[ 7.750508] [<ffffffff81f5f169>] kernel_init_freeable+0x1f5/0x282
[ 7.758005] [<ffffffff818da36e>] kernel_init+0xe/0xe0
[ 7.764338] [<ffffffff818eefdf>] ret_from_fork+0x3f/0x70
[ 7.770961]
-> #0 (&cpu_hotplug.rwsem){++++++}:
[ 7.776255] [<ffffffff81122817>] __lock_acquire+0x2207/0x2240
[ 7.783363] [<ffffffff811232b1>] lock_acquire+0xd1/0x290
[ 7.789986] [<ffffffff810cb6e2>] get_online_cpus+0x62/0xb0
[ 7.796805] [<ffffffff810ebd63>] apply_workqueue_attrs+0x183/0x4b0
[ 7.804398] [<ffffffff810ed7bc>] __alloc_workqueue_key+0x2ec/0x560
[ 7.811992] [<ffffffff815cbefa>] ttm_mem_global_init+0x5a/0x310
[ 7.819295] [<ffffffff815dcbb2>] mgag200_ttm_mem_global_init+0x12/0x20
[ 7.827277] [<ffffffff815c4df5>] drm_global_item_ref+0x65/0xe0
[ 7.834481] [<ffffffff815dcd90>] mgag200_mm_init+0x50/0x1c0
[ 7.841395] [<ffffffff815d757f>] mgag200_driver_load+0x30f/0x500
[ 7.848793] [<ffffffff815b1491>] drm_dev_register+0xb1/0x100
[ 7.855804] [<ffffffff815b428d>] drm_get_pci_dev+0x8d/0x1e0
[ 7.862715] [<ffffffff815dbd3f>] mga_pci_probe+0x9f/0xc0
[ 7.869338] [<ffffffff814bde92>] local_pci_probe+0x42/0xa0
[ 7.876159] [<ffffffff810e54e8>] work_for_cpu_fn+0x18/0x30
[ 7.882979] [<ffffffff810e9d57>] process_one_work+0x1e7/0x7e0
[ 7.890087] [<ffffffff810ea518>] worker_thread+0x1c8/0x460
[ 7.896907] [<ffffffff810f05b6>] kthread+0xf6/0x110
[ 7.903043] [<ffffffff818eefdf>] ret_from_fork+0x3f/0x70
[ 7.909673]
[ 7.909673] other info that might help us debug this:
[ 7.909673]
[ 7.918616] Chain exists of:
&cpu_hotplug.rwsem --> drm_global_mutex --> &item->mutex
[ 7.927907] Possible unsafe locking scenario:
[ 7.927907]
[ 7.934521] CPU0 CPU1
[ 7.939580] ---- ----
[ 7.944639] lock(&item->mutex);
[ 7.948359] lock(drm_global_mutex);
[ 7.955292] lock(&item->mutex);
[ 7.961855] lock(&cpu_hotplug.rwsem);
[ 7.966158]
[ 7.966158] *** DEADLOCK ***
[ 7.966158]
[ 7.972771] 4 locks held by kworker/0:1/215:
[ 7.977539] #0: ("events"){.+.+.+}, at: [<ffffffff810e9cc6>] process_one_work+0x156/0x7e0
[ 7.986929] #1: ((&wfc.work)){+.+.+.}, at: [<ffffffff810e9cc6>] process_one_work+0x156/0x7e0
[ 7.996600] #2: (drm_global_mutex){+.+.+.}, at: [<ffffffff815b1406>] drm_dev_register+0x26/0x100
[ 8.006690] #3: (&item->mutex){+.+.+.}, at: [<ffffffff815c4dc3>] drm_global_item_ref+0x33/0xe0
[ 8.016559]
[ 8.016559] stack backtrace:
[ 8.021427] CPU: 0 PID: 215 Comm: kworker/0:1 Not tainted 4.1.0-02756-ge3d06bd-dirty #185
[ 8.030565] Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
[ 8.042034] Workqueue: events work_for_cpu_fn
[ 8.046909] ffffffff82857e30 ffff88042b3437c8 ffffffff818e5189 0000000000000011
[ 8.055216] ffffffff8282aa40 ffff88042b343818 ffffffff8111ee76 0000000000000004
[ 8.063522] ffff88042b343888 ffff88042b33f040 0000000000000004 ffff88042b33f040
[ 8.071827] Call Trace:
[ 8.074559] [<ffffffff818e5189>] dump_stack+0x4c/0x6e
[ 8.080300] [<ffffffff8111ee76>] print_circular_bug+0x1c6/0x220
[ 8.087011] [<ffffffff81122817>] __lock_acquire+0x2207/0x2240
[ 8.093528] [<ffffffff811232b1>] lock_acquire+0xd1/0x290
[ 8.099559] [<ffffffff810ebd63>] ? apply_workqueue_attrs+0x183/0x4b0
[ 8.106755] [<ffffffff810cb6e2>] get_online_cpus+0x62/0xb0
[ 8.112981] [<ffffffff810ebd63>] ? apply_workqueue_attrs+0x183/0x4b0
[ 8.120176] [<ffffffff810ead27>] ? alloc_workqueue_attrs+0x27/0x80
[ 8.127178] [<ffffffff810ebd63>] apply_workqueue_attrs+0x183/0x4b0
[ 8.134182] [<ffffffff8111cc21>] ? debug_mutex_init+0x31/0x40
[ 8.140690] [<ffffffff810ed7bc>] __alloc_workqueue_key+0x2ec/0x560
[ 8.147691] [<ffffffff815cbefa>] ttm_mem_global_init+0x5a/0x310
[ 8.154405] [<ffffffff8122b050>] ? __kmalloc+0x5e0/0x630
[ 8.160435] [<ffffffff815c4de2>] ? drm_global_item_ref+0x52/0xe0
[ 8.167243] [<ffffffff815dcbb2>] mgag200_ttm_mem_global_init+0x12/0x20
[ 8.174631] [<ffffffff815c4df5>] drm_global_item_ref+0x65/0xe0
[ 8.181245] [<ffffffff815dcd90>] mgag200_mm_init+0x50/0x1c0
[ 8.187570] [<ffffffff815d757f>] mgag200_driver_load+0x30f/0x500
[ 8.194383] [<ffffffff815b1491>] drm_dev_register+0xb1/0x100
[ 8.200802] [<ffffffff815b428d>] drm_get_pci_dev+0x8d/0x1e0
[ 8.207125] [<ffffffff818ebf9e>] ? mutex_unlock+0xe/0x10
[ 8.213156] [<ffffffff815dbd3f>] mga_pci_probe+0x9f/0xc0
[ 8.219187] [<ffffffff814bde92>] local_pci_probe+0x42/0xa0
[ 8.225412] [<ffffffff8111db81>] ? __lock_is_held+0x51/0x80
[ 8.231736] [<ffffffff810e54e8>] work_for_cpu_fn+0x18/0x30
[ 8.237962] [<ffffffff810e9d57>] process_one_work+0x1e7/0x7e0
[ 8.244477] [<ffffffff810e9cc6>] ? process_one_work+0x156/0x7e0
[ 8.251187] [<ffffffff810ea518>] worker_thread+0x1c8/0x460
[ 8.257410] [<ffffffff810ea350>] ? process_one_work+0x7e0/0x7e0
[ 8.264120] [<ffffffff810ea350>] ? process_one_work+0x7e0/0x7e0
[ 8.270829] [<ffffffff810f05b6>] kthread+0xf6/0x110
[ 8.276375] [<ffffffff818ee230>] ? _raw_spin_unlock_irq+0x30/0x60
[ 8.283282] [<ffffffff810f04c0>] ? kthread_create_on_node+0x220/0x220
[ 8.290566] [<ffffffff818eefdf>] ret_from_fork+0x3f/0x70
[ 8.296597] [<ffffffff810f04c0>] ? kthread_create_on_node+0x220/0x220
--
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