| Message ID | 1412887906-22533-1-git-send-email-kamal@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index a965665..36d0440 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1287,6 +1287,9 @@ static void remove_siblinginfo(int cpu) for_each_cpu(sibling, cpu_sibling_mask(cpu)) cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling)); + for_each_cpu(sibling, cpu_llc_shared_mask(cpu)) + cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling)); + cpumask_clear(cpu_llc_shared_mask(cpu)); cpumask_clear(cpu_sibling_mask(cpu)); cpumask_clear(cpu_core_mask(cpu)); c->phys_proc_id = 0;
This is a note to let you know that I have just added a patch titled sched: Fix unreleased llc_shared_mask bit during CPU hotplug to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue This patch is scheduled to be released in version 3.13.11.9. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.13.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From d63c9d72fd0fc68a7ff6023b76ffc8f156fc6550 Mon Sep 17 00:00:00 2001 From: Wanpeng Li <wanpeng.li@linux.intel.com> Date: Wed, 24 Sep 2014 16:38:05 +0800 Subject: sched: Fix unreleased llc_shared_mask bit during CPU hotplug commit 03bd4e1f7265548832a76e7919a81f3137c44fd1 upstream. The following bug can be triggered by hot adding and removing a large number of xen domain0's vcpus repeatedly: BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 IP: [..] find_busiest_group PGD 5a9d5067 PUD 13067 PMD 0 Oops: 0000 [#3] SMP [...] Call Trace: load_balance ? _raw_spin_unlock_irqrestore idle_balance __schedule schedule schedule_timeout ? lock_timer_base schedule_timeout_uninterruptible msleep lock_device_hotplug_sysfs online_store dev_attr_store sysfs_write_file vfs_write SyS_write system_call_fastpath Last level cache shared mask is built during CPU up and the build_sched_domain() routine takes advantage of it to setup the sched domain CPU topology. However, llc_shared_mask is not released during CPU disable, which leads to an invalid sched domainCPU topology. This patch fix it by releasing the llc_shared_mask correctly during CPU disable. Yasuaki also reported that this can happen on real hardware: https://lkml.org/lkml/2014/7/22/1018 His case is here: == Here is an example on my system. My system has 4 sockets and each socket has 15 cores and HT is enabled. In this case, each core of sockes is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-44, 90-104 Socket#3 | 45-59, 105-119 Then llc_shared_mask of CPU#30 has 0x3fff80000001fffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-44 and 90-104. When hot-removing socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 But llc_shared_mask is not cleared. So llc_shared_mask of CPU#30 remains having 0x3fff80000001fffc0000000. After that, when hot-adding socket#2 and #3, each core of sockets is numbered as follows: | CPU# Socket#0 | 0-14 , 60-74 Socket#1 | 15-29, 75-89 Socket#2 | 30-59 Socket#3 | 90-119 Then llc_shared_mask of CPU#30 becomes 0x3fff8000fffffffc0000000. It means that last level cache of Socket#2 is shared with CPU#30-59 and 90-104. So the mask has the wrong value. Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> Tested-by: Linn Crosetto <linn@hp.com> Reviewed-by: Borislav Petkov <bp@suse.de> Reviewed-by: Toshi Kani <toshi.kani@hp.com> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Steven Rostedt <srostedt@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1411547885-48165-1-git-send-email-wanpeng.li@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- arch/x86/kernel/smpboot.c | 3 +++ 1 file changed, 3 insertions(+) -- 1.9.1