[tip:x86/cpu] x86/topology: Use total_cpus for max logical packages calculation

From: tip-bot for Hui Wang
Date: Tue Dec 18 2018 - 07:43:06 EST


Commit-ID: aa02ef099cff042c2a9109782ec2bf1bffc955d4
Gitweb: https://git.kernel.org/tip/aa02ef099cff042c2a9109782ec2bf1bffc955d4
Author: Hui Wang <john.wanghui@xxxxxxxxxx>
AuthorDate: Wed, 7 Nov 2018 10:36:43 +0800
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 18 Dec 2018 13:38:37 +0100

x86/topology: Use total_cpus for max logical packages calculation

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@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: <guijianfeng@xxxxxxxxxx>
Cc: <wencongyang2@xxxxxxxxxx>
Cc: <douliyang1@xxxxxxxxxx>
Cc: <qiaonuohan@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20181107023643.22174-1-john.wanghui@xxxxxxxxxx

---
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 a9134d1910b9..ccd1f2a8e557 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1347,7 +1347,7 @@ 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);
}