From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 9 May 2024 18:43:05 +0000 (-0400)
Subject: page alloc wrapper: Fix get_pfnblock_flags_mask prototype
X-Git-Tag: v2.12.17~1
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=7a03a49a221efa744ef2de0562dcd24cde911603;p=lttng-modules.git

page alloc wrapper: Fix get_pfnblock_flags_mask prototype

The canary __canary__get_pfnblock_flags_mask has never done its job of
detecting changes to the prototype of get_pfnblock_flags_mask because
it was actually calling the wrapper, because the wrapper/page_alloc.h
header maps get_pfnblock_flags_mask to wrapper_get_pfnblock_flags_mask.

Unfortunately, this wrapper is included by page_alloc.c only _after_ the
linux/pageblock-flags.h header is included, which means the
get_pfnblock_flags_mask prototype does _not_ have the wrapper prefix,
which prevents it from being useful for any kind of type validation.

This has been detected by a compiler warning stating that
wrapper_get_pfnblock_flags_mask() does not have a prior declaration.

Move the wrapper/page_alloc.h include _before_ including
pageblock-flags.h. This ensures the declaration has the wrapper_ prefix,
and therefore the compiler compares the declaration with the definition
of wrapper_get_pfnblock_flags_mask within page_alloc.c. The canary
function can be removed because it is redundant with this type check.

With this proper type check in place, we notice the following two
changes upstream:

commit 535b81e209219 ("mm/page_alloc.c: remove unnecessary end_bitidx for [set|get]_pfnblock_flags_mask()")
introduced in v5.9 removes the end_bitidx argument.

commit ca891f41c4c79 ("mm: constify get_pfnblock_flags_mask and get_pfnblock_migratetype")
introduced in v5.14 adds a const qualifier to the struct page pointer.

Adapt the code to match the evolution of this prototype.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I51b7871edfbff0f74ba1cf4d0ad988eb8d642b4e
---

diff --git a/wrapper/page_alloc.c b/wrapper/page_alloc.c
index b464f4d1..3353eed7 100644
--- a/wrapper/page_alloc.c
+++ b/wrapper/page_alloc.c
@@ -18,12 +18,51 @@
 		|| LTTNG_DEBIAN_KERNEL_RANGE(3,16,7,9,0,0, 3,17,0,0,0,0) \
 		|| LTTNG_UBUNTU_KERNEL_RANGE(3,16,7,34, 3,17,0,0)))
 
+/* Include page_alloc wrapper before pageblock-flags.h. */
+#include <wrapper/page_alloc.h>
+
+#include <linux/pageblock-flags.h>
 #include <linux/kallsyms.h>
 #include <linux/mm_types.h>
 #include <linux/module.h>
 #include <wrapper/kallsyms.h>
-#include <wrapper/page_alloc.h>
+#include <lttng-kernel-version.h>
+
+#if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,14,0))
+static
+unsigned long (*get_pfnblock_flags_mask_sym)(const struct page *page,
+		unsigned long pfn,
+		unsigned long mask);
+
+unsigned long wrapper_get_pfnblock_flags_mask(const struct page *page,
+		unsigned long pfn,
+		unsigned long mask)
+{
+	WARN_ON_ONCE(!get_pfnblock_flags_mask_sym);
+	if (get_pfnblock_flags_mask_sym) {
+		return get_pfnblock_flags_mask_sym(page, pfn, mask);
+	} else {
+		return -ENOSYS;
+	}
+}
+#elif (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,9,0))
+static
+unsigned long (*get_pfnblock_flags_mask_sym)(struct page *page,
+		unsigned long pfn,
+		unsigned long mask);
 
+unsigned long wrapper_get_pfnblock_flags_mask(struct page *page,
+		unsigned long pfn,
+		unsigned long mask)
+{
+	WARN_ON_ONCE(!get_pfnblock_flags_mask_sym);
+	if (get_pfnblock_flags_mask_sym) {
+		return get_pfnblock_flags_mask_sym(page, pfn, mask);
+	} else {
+		return -ENOSYS;
+	}
+}
+#else	/* #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,9,0)) */
 static
 unsigned long (*get_pfnblock_flags_mask_sym)(struct page *page,
 		unsigned long pfn,
@@ -42,6 +81,8 @@ unsigned long wrapper_get_pfnblock_flags_mask(struct page *page,
 		return -ENOSYS;
 	}
 }
+#endif /* #else #if (LTTNG_LINUX_VERSION_CODE >= LTTNG_KERNEL_VERSION(5,9,0)) */
+
 EXPORT_SYMBOL_GPL(wrapper_get_pfnblock_flags_mask);
 
 int wrapper_get_pfnblock_flags_mask_init(void)
@@ -54,25 +95,6 @@ int wrapper_get_pfnblock_flags_mask_init(void)
 }
 EXPORT_SYMBOL_GPL(wrapper_get_pfnblock_flags_mask_init);
 
-/*
- * Canary function to check for 'get_pfnblock_flags_mask()' at compile time.
- *
- * From 'include/linux/pageblock-flags.h':
- *
- *   unsigned long get_pfnblock_flags_mask(struct page *page,
- *                                         unsigned long pfn,
- *                                         unsigned long end_bitidx,
- *                                         unsigned long mask);
- */
-__attribute__((unused)) static
-unsigned long __canary__get_pfnblock_flags_mask(struct page *page,
-						unsigned long pfn,
-						unsigned long end_bitidx,
-						unsigned long mask)
-{
-	return get_pfnblock_flags_mask(page, pfn, end_bitidx, mask);
-}
-
 #else
 
 #include <linux/pageblock-flags.h>