On Tue, Apr 17, 2018 at 10:47 AM, Dave Young <dyoung@xxxxxxxxxx> wrote: > 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? Yes, I have sent out the v2 patchset to explain the background better and also capture some details on where I found this patchset handy. Also added some dtb dumps logs from 'kexec -p -d' for reference (with this patchset applied) for clarity. You can view the v2 here <http://lists.infradead.org/pipermail/kexec/2018-April/020532.html> Regards, Bhupesh >> 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
