Messages in this thread | | | Date | Thu, 29 Jan 2015 13:14:17 -0800 | From | santosh shilimkar <> | Subject | Re: [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug() |
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On 1/29/2015 12:38 AM, Viresh Kumar wrote: > Looks like you just save my time here, Santosh has also reported a > similar race in a personal mail.. > > On 29 January 2015 at 12:12, Ethan Zhao <ethan.zhao@oracle.com> wrote: >> There is race observed between PPC changed notification handler worker thread >> and vcpu_hotplug() called within xenbus_thread() context. >> It is shown as following WARNING: >> >> ------------[ cut here ]------------ >> WARNING: CPU: 0 PID: 4 at include/linux/kref.h:47 >> kobject_get+0x41/0x50() >> Modules linked in: acpi_cpufreq(+) nfsd auth_rpcgss nfs_acl >> lockd grace sunrpc xfs libcrc32c sd_mod ixgbe igb mdio ahci hwmon >> ... >> [ 14.003548] CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted >> ... >> [ 14.003553] Workqueue: kacpi_notify acpi_os_execute_deferred >> [ 14.003554] 0000000000000000 000000008c76682c ffff88094c793af8 >> ffffffff81661b14 >> [ 14.003556] 0000000000000000 0000000000000000 ffff88094c793b38 >> ffffffff81072b61 >> [ 14.003558] ffff88094c793bd8 ffff8812491f8800 0000000000000292 >> 0000000000000000 >> [ 14.003560] Call Trace: >> [ 14.003567] [<ffffffff81661b14>] dump_stack+0x46/0x58 >> [ 14.003571] [<ffffffff81072b61>] warn_slowpath_common+0x81/0xa0 >> [ 14.003572] [<ffffffff81072c7a>] warn_slowpath_null+0x1a/0x20 >> [ 14.003574] [<ffffffff812e16d1>] kobject_get+0x41/0x50 >> [ 14.003579] [<ffffffff815262a5>] cpufreq_cpu_get+0x75/0xc0 >> [ 14.003581] [<ffffffff81527c3e>] cpufreq_update_policy+0x2e/0x1f0 >> [ 14.003586] [<ffffffff810b8cb2>] ? up+0x32/0x50 >> [ 14.003589] [<ffffffff81381aa9>] ? acpi_ns_get_node+0xcb/0xf2 >> [ 14.003591] [<ffffffff81381efd>] ? acpi_evaluate_object+0x22c/0x252 >> [ 14.003593] [<ffffffff813824f6>] ? acpi_get_handle+0x95/0xc0 >> [ 14.003596] [<ffffffff81360967>] ? acpi_has_method+0x25/0x40 >> [ 14.003601] [<ffffffff81391e08>] acpi_processor_ppc_has_changed+0x77/0x82 >> [ 14.003604] [<ffffffff81089566>] ? move_linked_works+0x66/0x90 >> [ 14.003606] [<ffffffff8138e8ed>] acpi_processor_notify+0x58/0xe7 >> [ 14.003609] [<ffffffff8137410c>] acpi_ev_notify_dispatch+0x44/0x5c >> [ 14.003611] [<ffffffff8135f293>] acpi_os_execute_deferred+0x15/0x22 >> [ 14.003614] [<ffffffff8108c910>] process_one_work+0x160/0x410 >> [ 14.003616] [<ffffffff8108d05b>] worker_thread+0x11b/0x520 >> [ 14.003617] [<ffffffff8108cf40>] ? rescuer_thread+0x380/0x380 >> [ 14.003621] [<ffffffff81092421>] kthread+0xe1/0x100 >> [ 14.003623] [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0 >> [ 14.003628] [<ffffffff81669ebc>] ret_from_fork+0x7c/0xb0 >> [ 14.003630] [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0 >> [ 14.003631] ---[ end trace 89e66eb9795efdf7 ]--- >> >> Thread A: Workqueue: kacpi_notify >> >> acpi_processor_notify() >> acpi_processor_ppc_has_changed() >> cpufreq_update_policy() >> cpufreq_cpu_get() >> kobject_get() >> >> Thread B: xenbus_thread() >> >> xenbus_thread() >> msg->u.watch.handle->callback() >> handle_vcpu_hotplug_event() >> vcpu_hotplug() >> cpu_down() >> __cpu_notify(CPU_DOWN_PREPARE..) >> cpufreq_cpu_callback() >> __cpufreq_remove_dev_prepare() >> update_policy_cpu() >> kobject_move() > > Where is the race ? How do you say this is racy ? > > I am not sure if the problem is with kobject_move(), to me it looked like > the problem is with cpufreq_policy_put_kobj() and we tried to do kobject_get() > after the kobject has been freed.. > > I don't agree to the solution you gave, but lets first make sure what the > problem is, and then take any action against it. > > Please try this patch and let us know if it fixes it for you: > Yes it does fix the issue. Thanks Viresh
Regards, Santosh
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