On Mon, Jan 16, 2017 at 1:53 AM, zhouchengming <zhouchengmi...@huawei.com> wrote: > On 2017/1/16 17:05, Thomas Gleixner wrote: >> >> On Mon, 16 Jan 2017, Zhou Chengming wrote: >> >> Can you please stop sending the same patch over and over every other day? >> >> Granted, things get forgotten, but sending a polite reminder after a week >> is definitely enough. >> >> Maintainers are not machines responding within a split second on every >> mail >> they get. And that patch is not so substantial that it justifies that kind >> of spam. >> > > Very sorry for the noise. We are just not sure this is the right fix because > it's > hard to reproduce. > I believe this is the right fixed. I tried it and instrumented the code to verify thread_id assignment. The problem is easy to reproduce.
$ echo 0 >/sys/devices/system/cpu/cpu2/online $ echo 1 >/sys/devices/system/cpu/cpu2/online Normally on Haswell Desktop part, CPU2 gets thread_id 0 on boot, CPU6 gets thread_id 1. If you offline CPU2 and bring it back in, it will get thread_id 1 and thus both sibling will point to the same exclusive state. The fix is, indeed, to check if the sibling is not already assigned 1, and if so to keep 0 for the CPU being online'd.
