On Fri, May 29, 2026 at 01:27:12PM +0530, Shrikanth Hegde wrote:
> Venkat Reported a boot kernel panic next-20260522. Git bisect pointed to
> b5ea300a17e3 ("sched/cache: Make LLC id continuous")
>
> Stacktrace points to llc_mask being null.
>
> NIP [c000000000e58504] _find_first_bit+0x44/0x130
> LR [c000000000e58500] _find_first_bit+0x40/0x130
> Call Trace:
> build_sched_domains+0xad8/0xe50
> sched_init_smp+0xa8/0x164
> kernel_init_freeable+0x250/0x370
> ret_from_kernel_user_thread+0x14/0x1c
>
> On powerpc, cpu_coregroup_mask is available only when the underlying
> hardware support coregroup. In shared LPAR, QEMU guest or power9 etc
> coregroup isn't supported. In such cases llc_mask was being referenced
> when it was null leading to panic.
>
> On powerpc, LLC is at SMT core level. So assumption that coregroup(MC)
> domain point to LLC is wrong. Provide a way for archs to say where its
> LLC is if it not at MC domain.
>
> Based on tip/master at 5c89783224e9 ("Merge branch into tip/master:
> 'x86/tdx'")
> Cc: [email protected]
This seems unwarranted, the patch breaking stuff is in tip:sched/core.
> Fixes: b5ea300a17e3 ("sched/cache: Make LLC id continuous")
> Reported-by: Venkat Rao Bagalkote <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Reviewed-by: Chen Yu <[email protected]>
> Tested-by: Venkat Rao Bagalkote <[email protected]>
> Tested-by: Ritesh Harjani (IBM) <[email protected]>
> Co-developed-by: Chen, Yu C <[email protected]>
> Signed-off-by: Shrikanth Hegde <[email protected]>
Thanks all! I'll stick this in tip:sched/core to go along with the
patches that broke stuff.
