From: Hui Wang john.wanghui@huawei.com
[ Upstream commit aa02ef099cff042c2a9109782ec2bf1bffc955d4 ]
nr_cpu_ids can be limited on the command line via nr_cpus=. This can break the logical package management because it results in a smaller number of packages while in kdump kernel.
Check below case: There is a two sockets system, each socket has 8 cores, which has 16 logical cpus while HT was turn on.
0 1 2 3 4 5 6 7 | 16 17 18 19 20 21 22 23 cores on socket 0 threads on socket 0 8 9 10 11 12 13 14 15 | 24 25 26 27 28 29 30 31 cores on socket 1 threads on socket 1
While starting the kdump kernel with command line option nr_cpus=16 panic was triggered on one of the cpus 24-31 eg. 26, then online cpu will be 1-15, 26(cpu 0 was disabled in kdump), ncpus will be 16 and __max_logical_packages will be 1, but actually two packages were booted on.
This issue can reproduced by set kdump option nr_cpus=<real physical core numbers>, and then trigger panic on last socket's thread, for example:
taskset -c 26 echo c > /proc/sysrq-trigger
Use total_cpus which will not be limited by nr_cpus command line to calculate the value of __max_logical_packages.
Signed-off-by: Hui Wang john.wanghui@huawei.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: guijianfeng@huawei.com Cc: wencongyang2@huawei.com Cc: douliyang1@huawei.com Cc: qiaonuohan@huawei.com Link: https://lkml.kernel.org/r/20181107023643.22174-1-john.wanghui@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/smpboot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index f02ecaf97904..6489067b78a4 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1346,7 +1346,7 @@ void __init calculate_max_logical_packages(void) * extrapolate the boot cpu's data to all packages. */ ncpus = cpu_data(0).booted_cores * topology_max_smt_threads(); - __max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus); + __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus); pr_info("Max logical packages: %u\n", __max_logical_packages); }