On Thu, Aug 26, 2021 at 6:54 PM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Aug 26, 2021 at 06:23:53PM +0800, Woody Lin wrote: > > On Thu, Aug 26, 2021 at 5:48 PM Greg Kroah-Hartman > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Thu, Aug 26, 2021 at 05:28:54PM +0800, Woody Lin wrote: > > > > Add char device driver 'userpanic-dev' that exposes an interface to > > > > userspace processes to request a system panic with customized panic > > > > message. > > > > > > > > Signed-off-by: Woody Lin <woodylin@xxxxxxxxxx> > > > > --- > > > > drivers/staging/android/Kconfig | 12 +++ > > > > drivers/staging/android/Makefile | 1 + > > > > drivers/staging/android/userpanic-dev.c | 110 ++++++++++++++++++++++++ > > > > > > Why is this in staging? What is wrong with it that it can not just go > > > into the real part of the kernel? A TODO file is needed explaining what > > > needs to be done here in order for it to be accepted. > > > > Got it. No more TODO for this driver and I will move it to drivers/android/. > > > > > > > > But why is this really needed at all? Why would userspace want to panic > > > the kernel in yet-another-way? > > > > The idea is to panic the kernel with a panic message specified by the userspace > > process requesting the panic. Without this the panic handler can only collect > > panic message "sysrq triggered crash" for a panic triggered by user processes. > > Using this driver, user processes can put an informative description - > > process name, > > reason ...etc. - to the panic message. > > What custom userspace tool is going to use this new user/kernel api and > again, why is it needed? Who needs to panic the kernel with a custom > message and where is that used? It's for Android's services. Currently there are usages like these: * init requests panic in InitFatalReboot (abort handler). https://android.googlesource.com/platform/system/core/+/master/init/reboot_utils.cpp#170 android::base::WriteStringToFile("c", PROC_SYSRQ); * llkd requests panic to recover kernel live-lock. https://android.googlesource.com/platform/system/core/+/master/llkd/libllkd.cpp#564 android::base::WriteStringToFd("c", sysrqTriggerFd); * Watchdog requests panic to recover timeout-loop. https://android.googlesource.com/platform/frameworks/base/+/master/services/core/java/com/android/server/Watchdog.java#847 doSysRq('c'); So to improve the panic message from "sysrq triggered crash" to a more informative one (e.g.: "Watchdog break timeout-loop", "llkd panic live-lock"), we'd like to add this driver to expose a dedicated interface for userspace to panic the kernel with a custom message. Later the panic handler implemented per platform can collect the message and use it to build the crash report. A crash report with a more readable title (compared to the generic "sysrq triggered crash") will be easier to categorize, triage, etc. And the reason to submit this to upstream, instead of making it a vendor module, is that we'd like to enable it for the early stage of "init", where none of the kernel module has been mounted. > > thanks, > > greg k-h Regards, Woody
