From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 7 Oct 2024 14:30:49 +0000 (+0200)
Subject: mm: percpu: increase PERCPU_DYNAMIC_SIZE_SHIFT on certain builds.
X-Git-Tag: v6.12-rc4~32^2~22
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8f3ce3d996bf1e2f8474ec3ddabdb8765c19e6ea;p=thirdparty%2Fkernel%2Flinux.git

mm: percpu: increase PERCPU_DYNAMIC_SIZE_SHIFT on certain builds.

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.

Link: https://lkml.kernel.org/r/20241007143049.gyMpEu89@linutronix.de
Fixes: d8fccd9ca5f9 ("arm64: Allow to enable PREEMPT_RT.")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202410020326.iaZIteIx-lkp@intel.com/
Reported-by: Arnd Bergmann <arnd@kernel.org>
Closes: https://lore.kernel.org/20241004095702.637528-1-arnd@kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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