This Linux kernel change "x86: Fix list/memory corruption on CPU hotplug" is included in the Linux 3.15 release. This change is authored by Igor Mammedov <imammedo [at] redhat.com> on Thu Jun 5 15:42:43 2014 +0200. The commit for this change in Linux stable tree is 89f898c (patch).
x86: Fix list/memory corruption on CPU hotplug currently if AP wake up is failed, master CPU marks AP as not present in do_boot_cpu() by calling set_cpu_present(cpu, false). That leads to following list corruption on the next physical CPU hotplug: [ 418.107336] WARNING: CPU: 1 PID: 45 at lib/list_debug.c:33 __list_add+0xbe/0xd0() [ 418.115268] list_add corruption. prev->next should be next (ffff88003dc57600), but was ffff88003e20c3a0. (prev=ffff88003e20c3a0). [ 418.123693] Modules linked in: nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6t_REJECT ipt_REJECT cfg80211 xt_conntrack rfkill ee [ 418.138979] CPU: 1 PID: 45 Comm: kworker/u10:1 Not tainted 3.14.0-rc6+ #387 [ 418.149989] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007 [ 418.165750] Workqueue: kacpi_hotplug acpi_hotplug_work_fn [ 418.166433] 0000000000000021 ffff880038ca7988 ffffffff8159b22d 0000000000000021 [ 418.176460] ffff880038ca79d8 ffff880038ca79c8 ffffffff8106942c ffff880038ca79e8 [ 418.177453] ffff88003e20c3a0 ffff88003dc57600 ffff88003e20c3a0 00000000ffffffea [ 418.178445] Call Trace: [ 418.185811] [<ffffffff8159b22d>] dump_stack+0x49/0x5c [ 418.186440] [<ffffffff8106942c>] warn_slowpath_common+0x8c/0xc0 [ 418.187192] [<ffffffff81069516>] warn_slowpath_fmt+0x46/0x50 [ 418.191231] [<ffffffff8136ef51>] ? acpi_ns_get_node+0xb7/0xc7 [ 418.193889] [<ffffffff812f796e>] __list_add+0xbe/0xd0 [ 418.196649] [<ffffffff812e2aa9>] kobject_add_internal+0x79/0x200 [ 418.208610] [<ffffffff812e2e18>] kobject_add_varg+0x38/0x60 [ 418.213831] [<ffffffff812e2ef4>] kobject_add+0x44/0x70 [ 418.229961] [<ffffffff813e2c60>] device_add+0xd0/0x550 [ 418.234991] [<ffffffff813f0e95>] ? pm_runtime_init+0xe5/0xf0 [ 418.250226] [<ffffffff813e32be>] device_register+0x1e/0x30 [ 418.255296] [<ffffffff813e82a3>] register_cpu+0xe3/0x130 [ 418.266539] [<ffffffff81592be5>] arch_register_cpu+0x65/0x150 [ 418.285845] [<ffffffff81355c0d>] acpi_processor_hotadd_init+0x5a/0x9b ... Which is caused by the fact that generic_processor_info() allocates logical CPU id by calling: cpu = cpumask_next_zero(-1, cpu_present_mask); which returns id of previously failed to wake up CPU, since its bit is cleared by do_boot_cpu() and as result register_cpu() tries to register another CPU with the same id as already present but failed to be onlined CPU. Taking in account that AP will not do anything if master CPU failed to wake it up, there is no reason to mark that AP as not present and break next cpu hotplug attempts. As a side effect of not marking AP as not present, user would be allowed to online it again later. Also fix memory corruption in acpi_unmap_lsapic() if during CPU hotplug master CPU failed to wake up AP it set percpu x86_cpu_to_apicid to BAD_APICID=0xFFFF for AP. However following attempt to unplug that CPU will lead to out of bound write access to __apicid_to_node which is 32768 items long on x86_64 kernel. So with above fix of cpu_present_mask make sure that a present CPU has a valid APIC ID by not setting x86_cpu_to_apicid to BAD_APICID in do_boot_cpu() on failure and allow acpi_processor_remove()->acpi_unmap_lsapic() cleanly remove CPU. Signed-off-by: Igor Mammedov <firstname.lastname@example.org> Acked-by: Toshi Kani <email@example.com> Cc: Thomas Gleixner <firstname.lastname@example.org> Link: http://email@example.com Signed-off-by: Ingo Molnar <firstname.lastname@example.org>
There are 3 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.
arch/x86/kernel/smpboot.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 3482693..2988f69 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -859,9 +859,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) /* was set by cpu_init() */ cpumask_clear_cpu(cpu, cpu_initialized_mask); - - set_cpu_present(cpu, false); - per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID; } /* mark "stuck" area as not stuck */