On 04/16/18 at 08:39pm, Bhupesh Sharma wrote: > Hi Dave, > > On Mon, Apr 16, 2018 at 1:43 PM, Dave Young <dyoung@xxxxxxxxxx> wrote: > > Hi Bhupesh, > > > > On 04/03/18 at 07:28pm, Bhupesh Sharma wrote: > >> Hi James, > >> > >> Sorry for the delay, I had a long weekend last week. > >> > >> On Tue, Mar 27, 2018 at 7:01 PM, James Morse <james.morse@xxxxxxx> wrote: > >> > Hi Akashi, Bhupesh, > >> > > >> > On 27/03/18 10:04, AKASHI Takahiro wrote: > >> >> On Mon, Mar 26, 2018 at 02:29:31PM +0530, Bhupesh Sharma wrote: > >> >>> On Tue, Mar 20, 2018 at 12:36 AM, Bhupesh Sharma <bhsharma@xxxxxxxxxx> wrote: > >> >>>> On Mon, Mar 19, 2018 at 8:15 PM, AKASHI Takahiro > >> >>>> <takahiro.akashi@xxxxxxxxxx> wrote: > >> >>>>> On Mon, Mar 19, 2018 at 04:05:38PM +0530, Bhupesh Sharma wrote: > >> >>>>>> At several occasions it would be useful to dump the fdt > >> >>>>>> blob being passed to the second (kexec/kdump) kernel > >> >>>>>> when '-d' flag is specified while invoking kexec/kdump. > >> >>>>> > >> >>>>> Why not just save binary data to a file and interpret it > >> >>>>> with dtc command? > >> > > >> > I'd prefer this too. It would also let us debug any issue where kexec-tools > >> > produces an invalid DTB. It also lets us test booting the kernel from firmware > >> > with that DTB. > >> > >> I captured the use case where it is not possible to do so. I have seen > >> primary kernel crash before we can get to the command prompt to save > >> the dtb blob. Since the arm64 crashkernel still seems to have issues > >> itself while booting on acpi enabled machines (see > >> <https://www.spinics.net/lists/arm-kernel/msg616632.html>), so we are > >> trying to debug a problem which has two undefined variables :) > >> > >> >>>> Well, there are a couple of reasons for that which can be understood > >> >>>> from a system which is in a production environment (for e.g. I have > >> >>>> worked on one arm64 system in the past which used a yocto based > >> >>>> distribution in which kexec -p was launched with a -d option as a part > >> >>>> of initial ramfs scriptware): > >> > > >> > and panics before you get an interactive prompt or persistent storage? I think > >> > this would be a pretty niche use-case. You could always base64-dump the dtb to > >> > stdout from your script. > >> > >> That is pretty basic case on several new arm64 development boards > >> (e.g. qualcomm, huawei etc) where we are debugging issues in primary > >> kernel boot (and we are not even able to reach the command prompt). > >> > >> If the crashkernel crashes even before the primary kernel does because > >> of the issues in the way DTB is passed to the crashkernel (which can > >> include wrong DTB fields), we better have mechanisms to track the same > >> rather than adding debug prints to the kernels. > > > > In this case, since userspace always need to run 'kexec -l', there > > should be chance to save dtb and dump them in scripts if needed. > > If this is doable in scripts I also tend not to add the code in kexec-tools. > > Perhaps you missed my latest email which explained the use case better > (please see [1]). > Please note that I am talking about the 'kexec -p' or the kdump use > case rather than the 'kexec -l' or the warm reboot to the second > kernel. It is a typo, I meant about 'kexec -p' as well > > In several cases its useful if we are not able to reach the command > prompt to just modify the scriptware to launch 'kexec -p' when the > ramfs starts up so that we can catch crashes which happen before the > primary kernel reaches the command prompt. For example, on freescale > boards I found this scriptware mechanism quite useful on yocto based > distributions, as you can be porting a new upstream kernel on the > board and thus is not very stable while booting and the crashkernel > also has issues which causes it to crash. In such cases although we > see a panic message from the crashkernel it is very difficult to > deduce that it was because of some wrongly fixed up dtb property. Since kexec -p need to be automated in scripts, add something to dump dtb is also doable. > > Getting a debug log which contains the dtb dump is very useful in > above cases for debugging. > > Also saving the dtb requires 'dtc' tool to be installed which is an > additional dependency. I think it should be not a big problem, dtc is designed to do this. > > Since we have debug facility/messages already available when we > execute 'kexec -p' with '-d' flag we can use the dtb dumps from the > tool to debug crashes than happen in the crashkernel also because of > wrong dtb fields fixed up by 'kexec-tools'. I was loathe to keep this > patch locally and apply to the upstream 'kexec-tools' when debugging > these issues as I think it makes sense to improve our debugging > capabilities if we know there are issues around the same. Hmm, do you have the example kexec-tools fix-up the dtb content? > > Ok, let me resend this patch with a cover letter this time to explain > the use case better and also to capture the dtb logs. > > [1] https://marc.info/?l=kexec&m=152382169120505&w=2 Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
