(2014/09/23 15:36), Wanpeng Li wrote: > Hi Kamezawa, > 于 14-9-23 下午12:46, Kamezawa Hiroyuki 写道: >> (2014/09/17 16:17), Wanpeng Li wrote: >>> 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 >>> >>> This bug can be triggered by hot add and remove large number of xen >>> domain0's vcpus repeatedly. >>> >>> Last level cache shared map is built during cpu up and build sched domain >>> routine takes advantage of it to setup sched domain cpu topology, however, >>> llc shared map is unreleased during cpu disable which lead to invalid sched >>> domain cpu topology. This patch fix it by release llc shared map correctly >>> during cpu disable. >>> >>> Reviewed-by: Toshi Kani <toshi.k...@hp.com> >>> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com> >>> Tested-by: Linn Crosetto <l...@hp.com> >>> Signed-off-by: Wanpeng Li <wanpeng...@linux.intel.com> >> Yasuaki reported this can happen on our real hardware. >> https://lkml.org/lkml/2014/7/22/1018 >> >> Our case is here. >> == >> Here is a 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 wrong value. >> At first, I cleared hot-removed CPU number's bit from llc_shared_map >> when hot removing CPU. But Borislav suggested that the problem will >> disappear if readded CPU is assigned same CPU number. And llc_shared_map >> must not be changed. >> == >> >> So, please. > > As I mentioned before, we still observe calltrace after Yasuaki's patch > applied. > https://lkml.org/lkml/2014/7/29/40 > Yes. I just wanted to say we need your patch by showing real hardware case. Sorry for confusion I just reused his explanation of the problem.
I know Yasuaki's original trial was clearing llc_shared map as you do. > Actually I prefer to merge both patches, one for fix llc shared map > unreleased during hotplug and the other one for assign same CPU number > to readded CPU. > I agree. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
