> -----Original Message----- > From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx] > Sent: Thursday, February 12, 2015 2:28 PM > To: KY Srinivasan > Cc: Vitaly Kuznetsov; linux-kernel@xxxxxxxxxxxxxxx; Greg Kroah-Hartman; > Haiyang Zhang; Andrew Morton; Yasuaki Ishimatsu; Tang Chen; Vlastimil > Babka; David Rientjes; Fabian Frederick; Zhang Zhen; Vladimir Davydov; > Wang Nan; devel@xxxxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx > Subject: Re: [PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock > between memory adding and onlining > > On Thursday, February 12, 2015 10:01:48 PM KY Srinivasan wrote: > > > > > -----Original Message----- > > > From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx] > > > Sent: Thursday, February 12, 2015 2:13 PM > > > To: KY Srinivasan > > > Cc: Vitaly Kuznetsov; linux-kernel@xxxxxxxxxxxxxxx; Greg > > > Kroah-Hartman; Haiyang Zhang; Andrew Morton; Yasuaki Ishimatsu; Tang > > > Chen; Vlastimil Babka; David Rientjes; Fabian Frederick; Zhang Zhen; > > > Vladimir Davydov; Wang Nan; devel@xxxxxxxxxxxxxxxxxxxxxx; > > > linux-mm@xxxxxxxxx > > > Subject: Re: [PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock > > > between memory adding and onlining > > > > > > On Thursday, February 12, 2015 03:38:42 PM KY Srinivasan wrote: > > > > > > > > > -----Original Message----- > > > > > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > > > > > Sent: Thursday, February 12, 2015 2:24 AM > > > > > To: linux-kernel@xxxxxxxxxxxxxxx > > > > > Cc: Greg Kroah-Hartman; KY Srinivasan; Haiyang Zhang; Andrew > > > > > Morton; Yasuaki Ishimatsu; Tang Chen; Vlastimil Babka; David > > > > > Rientjes; Fabian Frederick; Zhang Zhen; Vladimir Davydov; Wang Nan; > Rafael J. > > > > > Wysocki; devel@xxxxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx > > > > > Subject: [PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock > > > > > between memory adding and onlining > > > > > > > > > > RESEND (with no changes) because Rafael J. Wysocki was missing > > > > > in recepients. > > > > > > > > > > If newly added memory is brought online with e.g. udev rule: > > > > > SUBSYSTEM=="memory", ACTION=="add", ATTR{state}="online" > > > > > the following deadlock is observed (and easily reproducable): > > > > > > > > > > First participant, worker thread doing add_memory(): > > > > > > > > > > [ 724.948846] kworker/0:1 D ffff88000412f9c8 13248 27 2 > > > 0x00000000 > > > > > [ 724.973543] Workqueue: events hot_add_req [hv_balloon] [ > > > > > 724.991736] > > > > > ffff88000412f9c8 0000000000000000 ffff88003fa1dc30 > > > > > 00000000000151c0 [ 725.019725] 0000000000000246 > > > > > ffff88000412ffd8 00000000000151c0 > > > > > ffff88003a77a4e0 [ 725.046486] ffff88003fa1dc30 > > > > > 00000001032a6000 > > > > > ffff88003a7ca838 ffff88003a7ca898 [ 725.072969] Call Trace: > > > > > [ 725.082690] [<ffffffff81aac0a9>] > > > > > schedule_preempt_disabled+0x29/0x70 > > > > > [ 725.103799] [<ffffffff81aae33b>] > > > > > mutex_lock_nested+0x14b/0x470 [ 725.122367] > > > > > [<ffffffff815ed773>] ? device_attach+0x23/0xb0 [ 725.140992] > > > > > [<ffffffff815ed773>] device_attach+0x23/0xb0 [ 725.159131] > > > > > [<ffffffff815ecba0>] bus_probe_device+0xb0/0xe0 [ 725.177055] > > > > > [<ffffffff815ea693>] device_add+0x443/0x650 [ 725.195558] > > > > > [<ffffffff815ea8be>] device_register+0x1e/0x30 [ 725.213133] > > > > > [<ffffffff81601790>] init_memory_block+0xd0/0xf0 [ 725.231533] > > > > > [<ffffffff816018f1>] register_new_memory+0xb1/0xd0 [ 725.250769] > > > > > [<ffffffff81a961cf>] __add_pages+0x13f/0x250 [ 725.269642] > > > > > [<ffffffff81063770>] ? arch_add_memory+0x70/0xf0 [ 725.288764] > > > > > [<ffffffff81063770>] arch_add_memory+0x70/0xf0 [ 725.306117] > > > > > [<ffffffff81a95f8f>] add_memory+0xef/0x1f0 [ 725.322466] > > > > > [<ffffffffa00293af>] hot_add_req+0x33f/0xf90 [hv_balloon] [ > > > > > 725.342777] [<ffffffff8109509f>] > > > > > process_one_work+0x1df/0x4e0 [ 725.361459] [<ffffffff8109502d>] ? > > > > > process_one_work+0x16d/0x4e0 [ 725.380390] [<ffffffff810954bb>] > > > > > worker_thread+0x11b/0x450 [ 725.397684] [<ffffffff810953a0>] ? > > > > > process_one_work+0x4e0/0x4e0 [ 725.416533] [<ffffffff8109ac33>] > > > > > kthread+0xf3/0x110 [ 725.433372] [<ffffffff8109ab40>] ? > > > > > kthread_create_on_node+0x240/0x240 > > > > > [ 725.453749] [<ffffffff81ab1dfc>] ret_from_fork+0x7c/0xb0 [ > > > > > 725.470994] [<ffffffff8109ab40>] ? > > > > > kthread_create_on_node+0x240/0x240 > > > > > [ 725.491469] 6 locks held by kworker/0:1/27: > > > > > [ 725.505037] #0: ("events"){......}, at: > > > > > [<ffffffff8109502d>] > > > > > process_one_work+0x16d/0x4e0 [ 725.533370] #1: > > > > > ((&dm_device.ha_wrk.wrk)){......}, at: [<ffffffff8109502d>] > > > > > process_one_work+0x16d/0x4e0 [ 725.565580] #2: > > > > > (mem_hotplug.lock){......}, at: [<ffffffff811e6525>] > > > > > mem_hotplug_begin+0x5/0x80 [ 725.594369] #3: > > > > > (mem_hotplug.lock#2){......}, at: [<ffffffff811e656f>] > > > > > mem_hotplug_begin+0x4f/0x80 [ 725.628554] #4: > > > > > (mem_sysfs_mutex){......}, at: [<ffffffff81601873>] > > > > > register_new_memory+0x33/0xd0 [ 725.658519] #5: > > > > > (&dev->mutex){......}, > > > > > at: [<ffffffff815ed773>] device_attach+0x23/0xb0 > > > > > > > > > > Second participant, udev: > > > > > > > > > > [ 725.750889] systemd-udevd D ffff88003b94fc68 14016 888 530 > > > > > 0x00000004 > > > > > [ 725.773767] ffff88003b94fc68 0000000000000000 > > > > > ffff8800034949c0 > > > > > 00000000000151c0 [ 725.798332] ffffffff8210d980 > > > > > ffff88003b94ffd8 > > > > > 00000000000151c0 ffff880037a69270 [ 725.822841] > > > > > ffff8800034949c0 > > > > > 0000000100000001 ffff8800034949c0 ffffffff81ff2b48 [ > > > > > 725.849184] Call > > > Trace: > > > > > [ 725.858987] [<ffffffff81aac0a9>] > > > > > schedule_preempt_disabled+0x29/0x70 > > > > > [ 725.879231] [<ffffffff81aae33b>] > > > > > mutex_lock_nested+0x14b/0x470 [ 725.897860] > > > > > [<ffffffff811e656f>] ? mem_hotplug_begin+0x4f/0x80 [ 725.916698] > > > > > [<ffffffff811e656f>] mem_hotplug_begin+0x4f/0x80 [ 725.935064] > > > > > [<ffffffff811e6525>] ? mem_hotplug_begin+0x5/0x80 [ 725.953464] > > > > > [<ffffffff81a9631b>] online_pages+0x3b/0x520 [ 725.971542] > > > > > [<ffffffff815eb0b3>] ? device_online+0x23/0xa0 [ 725.989207] > > > > > [<ffffffff81601524>] memory_subsys_online+0x64/0xc0 [ > > > > > 726.008513] [<ffffffff815eb0fd>] device_online+0x6d/0xa0 [ > > > > > 726.025579] [<ffffffff816012eb>] store_mem_state+0x5b/0xe0 [ > > > > > 726.043400] [<ffffffff815e8258>] dev_attr_store+0x18/0x30 [ > > > > > 726.060506] [<ffffffff8127a808>] sysfs_kf_write+0x48/0x60 [ > > > > > 726.077940] [<ffffffff81279d1b>] kernfs_fop_write+0x13b/0x1a0 [ > > > > > 726.099416] [<ffffffff811f9f67>] vfs_write+0xb7/0x1f0 [ > > > > > 726.115748] [<ffffffff811fabf8>] > > > > > SyS_write+0x58/0xd0 [ 726.131933] [<ffffffff81ab1ea9>] > > > > > system_call_fastpath+0x12/0x17 [ 726.150691] 7 locks held by > > > > > systemd- > > > > > udevd/888: > > > > > [ 726.165044] #0: (sb_writers#3){......}, at: > > > > > [<ffffffff811fa063>] > > > > > vfs_write+0x1b3/0x1f0 [ 726.192422] #1: (&of->mutex){......}, at: > > > > > [<ffffffff81279c46>] kernfs_fop_write+0x66/0x1a0 [ 726.220289] #2: > > > > > (s_active#60){......}, at: [<ffffffff81279c4e>] > > > > > kernfs_fop_write+0x6e/0x1a0 [ 726.249382] #3: > > > > > (device_hotplug_lock){......}, at: [<ffffffff815e9c15>] > > > > > lock_device_hotplug_sysfs+0x15/0x50 > > > > > [ 726.281901] #4: (&dev->mutex){......}, at: > > > > > [<ffffffff815eb0b3>] > > > > > device_online+0x23/0xa0 [ 726.308619] #5: > > > > > (mem_hotplug.lock){......}, > > > at: > > > > > [<ffffffff811e6525>] mem_hotplug_begin+0x5/0x80 [ 726.337994] > #6: > > > > > (mem_hotplug.lock#2){......}, at: [<ffffffff811e656f>] > > > > > mem_hotplug_begin+0x4f/0x80 > > > > > > > > > > In short: onlining grabs device lock and then tries to do > > > > > mem_hotplug_begin() while add_memory() is between > > > > > mem_hotplug_begin() and mem_hotplug_done() and it tries > grabbing > > > > > device lock. > > > > > > > > > > To my understanding ACPI memory hotplug doesn't have the same > > > > > issue as device_hotplug_lock is being grabbed when the ACPI device > is added. > > > > > > > > > > Solve the issue by grabbing device_hotplug_lock before doing > > > > > add_memory(). If we do that, lock_device_hotplug_sysfs() will > > > > > cause syscall retry which will eventually succeed. To support > > > > > the change we need to export lock_device_hotplug/ > > > > > unlock_device_hotplug. This approach can be completely wrong > though. > > > > > > > > This issue was first discovered by Andy Whitcroft: > > > > https://lkml.org/lkml/2014/3/14/451 > > > > I had sent patches based on Andy's analysis that did not affect > > > > the users of the kernel hot-add memory APIs: > > > > https://lkml.org/lkml/2014/12/2/662 > > > > > > > > This patch puts the burden where it needs to be and can address > > > > the issue > > > for all clients. > > > > > > That seems to mean that this series is not needed. Is that correct? > > > > This patch was never committed upstream and so the issue still is there. > > Well, I'm not sure what to do now to be honest. > > Is this series regarded as the right way to address the problem that > everybody is comfortable with? Or is it still under discussion? We need to solve this problem and that is not under discussion. I also believe this problem needs to be solved in a way that addresses the problem where it belongs - not in the users of the hot_add API. Both my solution and the one proposed by David https://lkml.org/lkml/2015/2/12/57 address this issue. You can select either patch and check it in. I just want the issue addressed and I am not married to the solution I proposed. K. Y > > Rafael ��.n������g��� �a��� �&ޖ)���)��h���&������梷���� �Ǟ�m������)������^�����������v���O��zf������