mm/page_alloc.c: allow error injection

Model call chain after should_failslab().  Likewise, we can now use a
kprobe to override the return value of should_fail_alloc_page() and inject
allocation failures into alloc_page*().

This will allow injecting allocation failures using the BCC tools even
without building kernel with CONFIG_FAIL_PAGE_ALLOC and booting it with a
fail_page_alloc= parameter, which incurs some overhead even when failures
are not being injected.  On the other hand, this patch adds an
unconditional call to should_fail_alloc_page() from page allocation
hotpath.  That overhead should be rather negligible with
CONFIG_FAIL_PAGE_ALLOC=n when there's no kprobe attached, though.

[[email protected]: changelog addition]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Benjamin Poirier <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Alexander Duyck <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/asm-generic/error-injection.h

@@ -8,6 +8,7 @@ enum {
 	EI_ETYPE_NULL,		/* Return NULL if failure */
 	EI_ETYPE_ERRNO,		/* Return -ERRNO if failure */
 	EI_ETYPE_ERRNO_NULL,	/* Return -ERRNO or NULL if failure */
+	EI_ETYPE_TRUE,		/* Return true if failure */
 };
 
 struct error_injection_entry {

mm/page_alloc.c

@@ -3131,7 +3131,7 @@ static int __init setup_fail_page_alloc(char *str)
 }
 __setup("fail_page_alloc=", setup_fail_page_alloc);
 
-static bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
+static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 {
 	if (order < fail_page_alloc.min_order)
 		return false;
@@ -3181,13 +3181,19 @@ late_initcall(fail_page_alloc_debugfs);
 
 #else /* CONFIG_FAIL_PAGE_ALLOC */
 
-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;
 }
 
 #endif /* CONFIG_FAIL_PAGE_ALLOC */
 
+static 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);
+
 /*
  * Return true if free base pages are above 'mark'. For high-order checks it
  * will return true of the order-0 watermark is reached and there is at least