On Wed, 2021-01-06 at 09:20 +0800, Can Guo wrote: > Hi Bean, > > On 2021-01-06 02:38, Bean Huo wrote: > > On Tue, 2021-01-05 at 09:07 +0800, Can Guo wrote: > > > On 2021-01-05 04:05, Bean Huo wrote: > > > > On Sat, 2021-01-02 at 05:59 -0800, Can Guo wrote: > > > > > + * @shutting_down: flag to check if shutdown has been > > > > > invoked > > > > > > > > I am not much sure if this flag is need, since once PM going in > > > > shutdown path, what will be returnded by pm_runtime_get_sync()? > > > > > > > > If pm_runtime_get_sync() will fail, just check its return. > > > > > > > > > > That depends. During/after shutdown, for UFS's case only, > > > pm_runtime_get_sync(hba->dev) will most likely return 0, > > > because it is already RUNTIME_ACTIVE, pm_runtime_get_sync() > > > will directly return 0... meaning you cannot count on it. > > > > > > Check Stanley's change - > > > https://lore.kernel.org/patchwork/patch/1341389/ > > > > > > Can Guo. > > > > Can, > > > > Thanks for pointing out that. > > > > Based on my understanding, that patch is redundent. maybe I > > misundestood Linux shutdown sequence. > > Sorry, do you mean Stanley's change is redundant? yes. > > > > > I checked the shutdown flow: > > > > 1. Set the "system_state" variable > > 2. Disable usermod to ensure that no user from userspace can start > > a > > request > > I hope it is like what you interpreted, but step #2 only stops > UMH(#265) > but not all user space activities. Whereas, UMH is for kernel space > calling > user space. Can, I did further study and homework on the Linux shutdown in the last few days. Yes, you are right, usermodehelper_disable() is to prevent executing the process from the kernel space. But I didn't reproduce this "maybe" race issue while shutdown. no matter how I torment my system, once Linux shutdown/halt/reboot starts, nobody can access the sysfs node. I create 10 processes in the user space and constantly access UFS sysfs node, also, fio is running in the background for the normal data read/write. there is a shutdown thread that will randomly trigger shutdown/halt/reboot. but no race issue appears. I don't know if this is a hypothetical issue(the race between shutdown flow and sysfs node access), it may not really exist in the Linux envriroment. everytime, the shutdonw flow will be: e10_sync_handler()->e10_svc()->do_e10_svc()->__do_sys_reboot()- >kernel_poweroff/kernel_halt()->device_shutdown()->platform_shutdown()- >ufshcd_platform_shutdown()->ufshcd_shutdown(). I think before going into the kernel shutdown, the userspace cannot issue new requests anymore. otherwise, this would be a big issue. pm_runtime_get_sync() will return 0 or failure while shutdown? the answer is not important now, maybe as you said, it is always 0. But in my testing, it didn't get there the system has been shutdown. Which means once shutdonw starts, sysfs node access path cannot reach pm_runtime_get_sync(). (note, I don't know if sysfs node access thread has been disabled or not) Responsibly say, I didn't reproduce this issue on my system (ubuntu), maybe you are using Android. I am not an expert on this topic, if you have the best idea on how to reproduce this issue. please please let me try. appreciate it!!!!! Thanks, Bean > > 264 system_state = state; > 265 usermodehelper_disable(); > 266 device_shutdown(); > > Thanks, > Can Guo.
