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 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. Regards, Wanpeng Li > 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/ -- 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/
