Arnd reported a build failure due to the BUILD_BUG_ON() statement in
alloc_kmem_cache_cpus(). The test
PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)
The factors that increase the right side of the equation:
- PAGE_SIZE > 4KiB increases KMALLOC_SHIFT_HIGH
- For the local_lock_t in kmem_cache_cpu:
- PREEMPT_RT adds an actual lock.
- LOCKDEP increases the size of the lock.
- LOCK_STAT adds additional bytes plus padding to the lockdep
structure.
The net difference with and without PREEMPT_RT is 88 bytes for the
lock_lock_t, 96 bytes for kmem_cache_cpu due to additional padding.
This is enough to exceed the 80KiB limit with 16KiB page size - the 8KiB
page size is fine.
Increase PERCPU_DYNAMIC_SIZE_SHIFT to 13 on configs with PAGE_SIZE larger
than 4KiB and LOCKDEP enabled.
Fixes: d8fccd9ca5f9 ("arm64: Allow to enable PREEMPT_RT.")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202410020326.iaZIteIx-lkp@xxxxxxxxx/
Reported-by: Arnd Bergmann <arnd@xxxxxxxxxx>
Closes: https://lore.kernel.org/20241004095702.637528-1-arnd@xxxxxxxxxx
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
include/linux/percpu.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index b6321fc491598..52b5ea663b9f0 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -41,7 +41,11 @@
PCPU_MIN_ALLOC_SHIFT)
#ifdef CONFIG_RANDOM_KMALLOC_CACHES
-#define PERCPU_DYNAMIC_SIZE_SHIFT 12
+# if defined(CONFIG_LOCKDEP) && !defined(CONFIG_PAGE_SIZE_4KB)
+# define PERCPU_DYNAMIC_SIZE_SHIFT 13
+# else
+# define PERCPU_DYNAMIC_SIZE_SHIFT 12
+#endif /* LOCKDEP and PAGE_SIZE > 4KiB */
#else
#define PERCPU_DYNAMIC_SIZE_SHIFT 10
#endif
--
2.45.2
