于 9/24/14, 4:24 PM, Yasuaki Ishimatsu 写道: > (2014/09/24 17:13), 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 repeatly. >> >> 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. >> >> Yasuaki also reported this can happen on their real hardware. >> https://lkml.org/lkml/2014/7/22/1018 >> >> His 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. > Please remove it. The description is not explanation for your patch.
Ok， ；-） Regards, Wanpeng Li > > Thanks, > Yasuaki Ishimatsu > >> Reviewed-by: Borislav Petkov <[email protected]> >> Reviewed-by: Toshi Kani <[email protected]> >> Reviewed-by: Yasuaki Ishimatsu <[email protected]> >> Tested-by: Linn Crosetto <[email protected]> >> Signed-off-by: Wanpeng Li <[email protected]> >> --- >> v5 -> v6: >> * add the real-hardware reports to the changelog >> v4 -> v5: >> * add the description when the bug can occur >> v3 -> v4: >> * simplify backtrace >> v2 -> v3: >> * simplify backtrace >> v1 -> v2: >> * fix subject line >> >> arch/x86/kernel/smpboot.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c >> index 5492798..0134ec7 100644 >> --- a/arch/x86/kernel/smpboot.c >> +++ b/arch/x86/kernel/smpboot.c >> @@ -1292,6 +1292,9 @@ 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; >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [email protected] > 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
