[PATCH 2/2] mm, page_alloc: put should_fail_alloc_page() back behing CONFIG_FAIL_PAGE_ALLOC

[Vlastimil Babka <vbabka@xxxxxxx>]

This mostly reverts commit af3b854492f3 ("mm/page_alloc.c: allow error
injection"). The commit made should_fail_alloc_page() a noinline
function that's always called from the page allocation hotpath,
even if it's empty because CONFIG_FAIL_PAGE_ALLOC is not enabled, and
there is no option to disable it and prevent the associated function
call overhead.

As with the preceding patch "mm, slab: put should_failslab back behind
CONFIG_SHOULD_FAILSLAB" and for the same reasons, put the
should_fail_alloc_page() back behind the config option. When enabled,
the ALLOW_ERROR_INJECTION and BTF_ID records are preserved so it's not
a complete revert.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 include/linux/fault-inject.h | 6 ++----
 kernel/bpf/verifier.c        | 2 ++
 mm/fail_page_alloc.c         | 4 +++-
 mm/page_alloc.c              | 6 ------
 4 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
index be6d0bc111ad..354413950d34 100644
--- a/include/linux/fault-inject.h
+++ b/include/linux/fault-inject.h
@@ -91,12 +91,10 @@ static inline void fault_config_init(struct fault_config *config,
 
 struct kmem_cache;
 
-bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
-
 #ifdef CONFIG_FAIL_PAGE_ALLOC
-bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
+bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
 #else
-static inline bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
+static inline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 {
 	return false;
 }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e455654f3b91..a81e18409ec9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21122,7 +21122,9 @@ BTF_SET_START(btf_non_sleepable_error_inject)
  * Assume non-sleepable from bpf safety point of view.
  */
 BTF_ID(func, __filemap_add_folio)
+#ifdef CONFIG_FAIL_PAGE_ALLOC
 BTF_ID(func, should_fail_alloc_page)
+#endif
 #ifdef CONFIG_FAILSLAB
 BTF_ID(func, should_failslab)
 #endif
diff --git a/mm/fail_page_alloc.c b/mm/fail_page_alloc.c
index b1b09cce9394..532851ce5132 100644
--- a/mm/fail_page_alloc.c
+++ b/mm/fail_page_alloc.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/fault-inject.h>
+#include <linux/error-injection.h>
 #include <linux/mm.h>
 
 static struct {
@@ -21,7 +22,7 @@ static int __init setup_fail_page_alloc(char *str)
 }
 __setup("fail_page_alloc=", setup_fail_page_alloc);
 
-bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
+bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 {
 	int flags = 0;
 
@@ -41,6 +42,7 @@ bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 
 	return should_fail_ex(&fail_page_alloc.attr, 1 << order, flags);
 }
+ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);
 
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9ecf99190ea2..91b7234f1d7e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3031,12 +3031,6 @@ struct page *rmqueue(struct zone *preferred_zone,
 	return page;
 }
 
-noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
-{
-	return __should_fail_alloc_page(gfp_mask, order);
-}
-ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);
-
 static inline long __zone_watermark_unusable_free(struct zone *z,
 				unsigned int order, unsigned int alloc_flags)
 {

-- 
2.45.2