On 07/02/19 at 09:41am, Baoquan He wrote: > On 07/02/19 at 06:51am, David Airlie wrote: > > On Wed, Jun 26, 2019 at 6:29 PM Baoquan He <bhe@xxxxxxxxxx> wrote: > > > > > > On 06/26/19 at 04:15pm, Baoquan He wrote: > > > > Hi Dave, > > > > > > > > We met an kdump kernel boot failure on a lenovo system. Kdump kernel > > > > failed to boot, but just reset to firmware to reboot system. And nothing > > > > is printed out. > > > > > > > > The machine is a big server, with 6T memory and many cpu, its graphic > > > > driver module is mgag200. > > > > > > > > When added 'earlyprintk=ttyS0' into kernel command line, it printed > > > > out only one line to console during kdump kernel booting: > > > > KASLR disabled: 'nokaslr' on cmdline. > > > > > > > > Then reset to firmware to reboot system. > > > > > > > > By further code debugging, the failure happened in > > > > arch/x86/boot/compressed/misc.c, during kernel decompressing stage. It's > > > > triggered by the vga printing. As you can see, in __putstr() of > > > > arch/x86/boot/compressed/misc.c, the code checks if earlyprintk= is > > > > specified, and print out to the target. And no matter if earlyprintk= is > > > > added or not, it will print to VGA. And printing to VGA caused it to > > > > reset to firmware. That's why we see nothing when didn't specify > > > > earlyprintk=, but see only one line of printing about the 'KASLR > > > > disabled'. > > > > > > Here I mean: > > > That's why we see nothing when didn't specify earlyprintk=, but see only > > > one line of printing about the 'KASLR disabled' message when > > > earlyprintk=ttyS0 added. > > > > Just to clarify, the original kernel is booted with mgag200 turned > > off, then kexec works, but if the original kernel loads mgag200, the > > kexec kernels resets hard when the VGA is used to write stuff out. > > Thanks for looking into this, Dave. > > Yeah, in fact the issue was found in kdump kernel. I haven't checked the > kexec jumping. Kexec jumping will call device_shutdown() to attempt to > shutdown all devices before jumping to the 2nd kernel. But kdump jumping > won't. > > > > > This *might* be fixable in the controlled kexec case, but having an > > mgag200 shutdown path that tries to put the gpu back into a state > > where VGA doesn't die, but for the uncontrolled kexec it'll still be a > > problem, since once the gpu is up and running and VGA is disabled, it > > doesn't expect to see anymore VGA transactions. > > Yes, I see. It should have been shutdown by device_shutdown() in kexec > case. The uncontrolled case, I guess you mean the kdump case. In > kdump case, we don't call device_shutdown() before jumping because the > 1st kernel has been in crashed state, we just want to switch to kdump > kernel asap. So wondering how other GPU/VGA device/driver bebahve, > currently haven't got report about them. Probably mgag200 is very new, > or we may not meet them. This issue was met on a new bought server. I assumed the vga writing only take effect when earlyprintk is provided. eg. earlyprintk=ttyS0, then x86 early decompress code will write to both vga and ttyS0. So if one does not use earlyprintk, he/she still get nothing. But if one provides earlyprintk, then he/she should provide a correct param he want, instead of blindly assume kernel will write to vga even if he use ttyS0. Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
