On 03/29/25 at 01:14am, Roberto Ricci wrote: > On 2025-01-27 10:42 +0800, Dave Young wrote: > > On Mon, 27 Jan 2025 at 10:39, Dave Young <[email protected]> wrote: > > > On 01/13/25 at 10:28pm, Roberto Ricci wrote: > > > > After rebooting the system via kexec, hibernating and rebooting the > > > > machine, this oops occurs: > > > > > > > [snip] > > > > > > > > I will send the kernel config and dmesg in replies to this email. > > > > > > > > > > I tried your config (removed some config driver related which is not > > > useful), but it can not boot on my kvm guest. > > > Firstly I saw a panic in ftrace path, then I rebuilt the kernel without > > > ftrace, it panicked again but in kvm related code path. > > > Both are not related to kexec at all so I suspect your bug is not kexec > > > specific. > > > > > > [snip] > > > > > > You can find the kernel config here (with the ftrace enabled): > > > https://people.redhat.com/~ruyang/snakeyear/panic-ftrace.config > > > > BTW, if I disable KASAN then kernel can boot, anyway kexec + > > hibernation works fine with a few tests, no panics. > > > > > > > > Thanks > > > Dave > > Hi, > > sorry for the late reply. I tried your modified config, but I'm getting > the same oops I originally reported. No idea why the oops is not > happening for you.
Not that oops is not happening in my side, I can't boot kernel built with you provided config on Fedora OS. > > Anyway, I performed yet another bisection, this time with just plain > defconfig plus CONFIG_KEXEC_FILE=y, and I got different results. > > Updated steps to reproduce: > 1. Boot kernel >= v6.8 in a virtual machine created with this command: > `qemu-system-x86_64 -enable-kvm -smp 1 -m 4.0G -hda disk.qcow2` > 2. Load the same kernel with: > `kexec --kexec-file-syscall -l /boot/vmlinuz-6.14.0 --initrd > /boot/initramfs-6.14.0.img --reuse-cmdline` > 3. Reboot (or call `kexec -e` directly) > 4. Hibernate and reboot: `printf reboot >/sys/power/disk && printf disk > >/sys/power/state` > 5. Upon resuming, three things could happen, depending on luck: OK, this is a little complicated. wondering why you need to do the hibernation and reboot. Just for curiosity. > 5a. A kernel oops: > ``` > [ 42.574201] BUG: kernel NULL pointer dereference, address: 0000000000000000 ...snip... > I will send config and dmesg in replies to this email. > > The bisection pointed to > b3ba234171cd kexec_file: load kernel at top of system RAM if required > > #regzbot introduced: b3ba234171cd0d58df0a13c262210ff8b5fd2830 > > Now that I think about it, this was the commit I found when I did the > very first bisection after I found the bug. But I could not get the same > result with subsequent bisections, so I didn't mention it in my original > report. > > When reverting b3ba234171cd on top of v6.14, merge conflicts must be > solved, I hope I did it right: I doubt how this caused the failure. I have several questions, could you help answer: 1) Can this problem be stably reproduced with kexec_file_load? 2) if answer to 1) is yes, can reverting b3ba234171cd fix it stably? 3) If answer to 1) and 2) is yes, does kexec_load works for you? Asking this because kexec_load interface defaults to put kexec kernel on top of system RAM which is equivalent to applying commit b3ba234171cd. 4) Can you add '-d' to 'kexec -l' to print more debugging message? 5) Can normal kexec trigger the failure? I mean operating kexec w/o the hibernation/resumption. > > ``` > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > index 3eedb8c226ad..3014be212afd 100644 > --- a/kernel/kexec_file.c > +++ b/kernel/kexec_file.c > @@ -614,10 +614,7 @@ static int kexec_walk_resources(struct kexec_buf *kbuf, > crashk_res.start, crashk_res.end, > kbuf, func); > #endif > - if (kbuf->top_down) > - return walk_system_ram_res_rev(0, ULONG_MAX, kbuf, func); > - else > - return walk_system_ram_res(0, ULONG_MAX, kbuf, func); > + return walk_system_ram_res(0, ULONG_MAX, kbuf, func); > } > > /** > ``` > > Applying this diff solves the problem for v6.14. >
