[PATCH 1/1] hugetlb: fix CONFIG_PADATA dependency for non-SMP system

[Gang Li <gang.li@linux.dev>]

Randy Dunlap and kernel test robot reported a warning:

```
WARNING: unmet direct dependencies detected for PADATA
  Depends on [n]: SMP [=n]
  Selected by [y]:
  - HUGETLBFS [=y] && (X86 [=y] || SPARC64 || ARCH_SUPPORTS_HUGETLBFS [=n] || BROKEN [=n]) && (SYSFS [=y] || SYSCTL [=n])
```

hugetlb parallelization depends on PADATA, and PADATA depends on SMP, so
when the SMP config is disabled, the dependency of hugetlb on padata
should be downgraded to single thread.

Fixes: f2f635264b98 ("hugetlb: have CONFIG_HUGETLBFS select CONFIG_PADATA")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://lore.kernel.org/lkml/ec5dc528-2c3c-4444-9e88-d2c48395b433@infradead.org/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402020454.6EPkP1hi-lkp@intel.com/
Signed-off-by: Gang Li <ligang.bdlg@bytedance.com>
```
Hi Andrew, this fix patch is based on mm/mm-unstable.
Thanks!
```
---
 fs/Kconfig   | 2 +-
 mm/hugetlb.c | 9 ++++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index 3abc107ab2fbd..f2bc73fc0417e 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -261,7 +261,7 @@ menuconfig HUGETLBFS
 	depends on X86 || SPARC64 || ARCH_SUPPORTS_HUGETLBFS || BROKEN
 	depends on (SYSFS || SYSCTL)
 	select MEMFD_CREATE
-	select PADATA
+	select PADATA if SMP
 	help
 	  hugetlbfs is a filesystem backing for HugeTLB pages, based on
 	  ramfs. For architectures that support it, say Y here and read
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bf3d5dfb921e6..1b01b244fb50b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3457,6 +3457,7 @@ static void __init gather_bootmem_prealloc_node(unsigned long start, unsigned lo
 
 static void __init gather_bootmem_prealloc(void)
 {
+#ifdef CONFIG_PADATA
 	struct padata_mt_job job = {
 		.thread_fn	= gather_bootmem_prealloc_node,
 		.fn_arg		= NULL,
@@ -3469,6 +3470,9 @@ static void __init gather_bootmem_prealloc(void)
 	};
 
 	padata_do_multithreaded(&job);
+#else
+	gather_bootmem_prealloc_node(0, 0, NULL);
+#endif
 }
 
 static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
@@ -3568,6 +3572,7 @@ static unsigned long __init hugetlb_gigantic_pages_alloc_boot(struct hstate *h)
 
 static unsigned long __init hugetlb_pages_alloc_boot(struct hstate *h)
 {
+#ifdef CONFIG_PADATA
 	struct padata_mt_job job = {
 		.fn_arg		= h,
 		.align		= 1,
@@ -3600,7 +3605,9 @@ static unsigned long __init hugetlb_pages_alloc_boot(struct hstate *h)
 	job.max_threads	= num_node_state(N_MEMORY) * 2;
 	job.min_chunk	= h->max_huge_pages / num_node_state(N_MEMORY) / 2;
 	padata_do_multithreaded(&job);
-
+#else
+	hugetlb_pages_alloc_boot_node(0, h->max_huge_pages, h);
+#endif
 	return h->nr_huge_pages;
 }
 
-- 
2.20.1