diff options
| author | Shrikanth Hegde <sshegde@linux.ibm.com> | 2026-05-29 13:27:12 +0530 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-05-29 12:43:15 +0200 |
| commit | 1eae219ea0e80eed83c129e8cae0f007843f1893 (patch) | |
| tree | 1c51a2c4206b4c93bfbd0a6f0a861af321d0d7eb /kernel | |
| parent | 5ad278dd20bdf59714443894d7b3044471af97d0 (diff) | |
sched/topology: Provide arch_llc_mask for cache aware scheduling
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.
Fixes: b5ea300a17e3 ("sched/cache: Make LLC id continuous")
Closes: https://lore.kernel.org/all/51154de7-3700-4cb4-82f2-1b3a8fa427f7@linux.ibm.com/
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Co-developed-by: Chen, Yu C <yu.c.chen@intel.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Tested-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://patch.msgid.link/20260529075712.1181039-1-sshegde@linux.ibm.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/topology.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index df2ceb54c970..622e2e01974c 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -2063,12 +2063,21 @@ const struct cpumask *tl_mc_mask(struct sched_domain_topology_level *tl, int cpu return cpu_coregroup_mask(cpu); } -#define llc_mask(cpu) cpu_coregroup_mask(cpu) +/* + * Majority of architectures have LLC at MC domain level with exception + * such as powerpc. Provide a way for arch to specify where its LLC is + * if it falls in exception category + */ +# ifndef arch_llc_mask +#define arch_llc_mask(cpu) cpu_coregroup_mask(cpu) +# endif #else -#define llc_mask(cpu) cpumask_of(cpu) +#define arch_llc_mask(cpu) cpumask_of(cpu) #endif +#define llc_mask(cpu) arch_llc_mask(cpu) + const struct cpumask *tl_pkg_mask(struct sched_domain_topology_level *tl, int cpu) { return cpu_node_mask(cpu); |