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X-OriginatorOrg: intel.com On 3/21/2026 11:36 AM, K Prateek Nayak wrote: > Hello Nathan, > > Thank you for the report. > > On 3/21/2026 5:28 AM, Nathan Chancellor wrote: >> $ cat kernel/configs/schedstats.config >> CONFIG_SCHEDSTATS=y > > Is the "schedstats.config" available somewhere? I tried these > steps on my end but couldn't reproduce the crash with my config. > > Also, are you saying it is necessary to enable CONFIG_SCHEDSTATS > to observe the crash? > >> >> $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- mrproper defconfig schedstats.config zImage >> >> $ curl -LSs https://github.com/ClangBuiltLinux/boot-utils/releases/download/20241120-044434/arm-rootfs.cpio.zst | zstd -d >rootfs.cpio >> >> $ qemu-system-arm \ >> -display none \ >> -nodefaults \ >> -no-reboot \ >> -machine virt \ >> -append 'console=ttyAMA0 earlycon' \ >> -kernel arch/arm/boot/zImage \ >> -initrd rootfs.cpio \ >> -m 1G \ >> -serial mon:stdio >> [ 0.000000] Booting Linux on physical CPU 0x0 >> [ 0.000000] Linux version 7.0.0-rc4-00017-g8e8e23dea43e (nathan@framework-amd-ryzen-maxplus-395) (arm-linux-gnueabi-gcc (GCC) 15.2.0, GNU ld (GNU Binutils) 2.45) #1 SMP Fri Mar 20 16:12:05 MST 2026 >> ... >> [ 0.031929] 8<--- cut here --- >> [ 0.031999] Unable to handle kernel NULL pointer dereference at virtual address 00000000 when write >> [ 0.032172] [00000000] *pgd=00000000 >> [ 0.032459] Internal error: Oops: 805 [#1] SMP ARM >> [ 0.032902] Modules linked in: >> [ 0.033466] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.0.0-rc4-00017-g8e8e23dea43e #1 VOLUNTARY >> [ 0.033658] Hardware name: Generic DT based system >> [ 0.033770] PC is at build_sched_domains+0x7d0/0x1628 > > For me, this points to: > > $ scripts/faddr2line vmlinux build_sched_domains+0x7d0/0x1628 I suppose we might need to use arm-linux-gnueabi-addr2line, just in case of miss-match. > build_sched_domains+0x7d0/0x1628: > find_next_bit_wrap at include/linux/find.h:455 > (inlined by) build_sched_groups at kernel/sched/topology.c:1255 > (inlined by) build_sched_domains at kernel/sched/topology.c:2603 > > which is the: > > span = sched_domain_span(sd); > > for_each_cpu_wrap(i, span, cpu) /* Here */ { > ... > } > > in build_sched_groups() so we are likely going off the allocated > cpumask size but before that, we do this in the caller: > > sd->span_weight = cpumask_weight(sched_domain_span(sd)); > > which should have crashed too if we had a NULL pointer in the > cpumask range. So I'm at a loss. Maybe the pc points to a > different location in your build? > A wild guess, the major change is that we access sd->span, before initializing the sd structure with *sd = { ... }. The sd is allocated via alloc_percpu() uninitialized, the span at the end of the sd structure remain uninitialized. It is unclear how cpumask_weight(sd->span) might be affected by this uninitialized state. Before this patch, after *sd = { ... } is executed, the contents of sd->span are explicitly set to 0, which might be safer? Thanks, Chenyu