linux-kernel - [PATCH v2 4/4] tools: testing: Use existing atomic.h for vma/maple tests

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Message-ID: <20250828-b4-vma-no-atomic-h-v2-4-02d146a58ed2@google.com>
Date: Thu, 28 Aug 2025 12:28:01 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>
Cc: linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org, 
	linux-mm@...ck.org, Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH v2 4/4] tools: testing: Use existing atomic.h for vma/maple tests

The shared userspace logic used for unit-testing maple tree and VMA code
currently has its own replacements for atomics helpers. This is not
needed as the necessary APIs already have userspace implementations in
the tools tree. Switching over to that allows deleting a bit of code.

Note that the implementation is different; while the version being
deleted here is implemented using liburcu, the existing version in tools
uses either x86 asm or compiler builtins. It's assumed that both are
equally likely to be correct.

The tools tree's version of atomic_t is a struct type while the version
being deleted was just a typedef of an integer. This means it's no
longer valid to call __sync_bool_compare_and_swap() directly on it. One
option would be to just peek into the struct and call it on the field,
but it seems a little cleaner to just use the corresponding atomic.h
API whic has been added recently. Now the fake mapping_map_writable() is
copied from the real one.

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 tools/testing/shared/linux/maple_tree.h |  6 ++----
 tools/testing/vma/linux/atomic.h        | 17 -----------------
 tools/testing/vma/vma_internal.h        | 12 +++---------
 3 files changed, 5 insertions(+), 30 deletions(-)

diff --git a/tools/testing/shared/linux/maple_tree.h b/tools/testing/shared/linux/maple_tree.h
index f67d47d32857cee296c2784da57825c9a31cd340..7d0fadef0f11624dbb110ad351aabdc79a19dcd2 100644
--- a/tools/testing/shared/linux/maple_tree.h
+++ b/tools/testing/shared/linux/maple_tree.h
@@ -1,7 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0+ */
-#define atomic_t int32_t
-#define atomic_inc(x) uatomic_inc(x)
-#define atomic_read(x) uatomic_read(x)
-#define atomic_set(x, y) uatomic_set(x, y)
+#include <linux/atomic.h>
+
 #define U8_MAX UCHAR_MAX
 #include "../../../../include/linux/maple_tree.h"
diff --git a/tools/testing/vma/linux/atomic.h b/tools/testing/vma/linux/atomic.h
deleted file mode 100644
index 788c597c4fdea7392307de93ff4459453b96179b..0000000000000000000000000000000000000000
--- a/tools/testing/vma/linux/atomic.h
+++ /dev/null
@@ -1,17 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-
-#ifndef _LINUX_ATOMIC_H
-#define _LINUX_ATOMIC_H
-
-#define atomic_t int32_t
-#define atomic_inc(x) uatomic_inc(x)
-#define atomic_read(x) uatomic_read(x)
-#define atomic_set(x, y) uatomic_set(x, y)
-#define U8_MAX UCHAR_MAX
-
-#ifndef atomic_cmpxchg_relaxed
-#define  atomic_cmpxchg_relaxed		uatomic_cmpxchg
-#define  atomic_cmpxchg_release         uatomic_cmpxchg
-#endif /* atomic_cmpxchg_relaxed */
-
-#endif	/* _LINUX_ATOMIC_H */
diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index f13354bf0a1e3839327da7927c4a7da1530a1693..437d2a1013be418c6d3e77534fa19b0ee1518c9b 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h
@@ -21,6 +21,7 @@
 
 #include <stdlib.h>
 
+#include <linux/atomic.h>
 #include <linux/list.h>
 #include <linux/maple_tree.h>
 #include <linux/mm.h>
@@ -1398,15 +1399,8 @@ static inline bool map_deny_write_exec(unsigned long old, unsigned long new)
 
 static inline int mapping_map_writable(struct address_space *mapping)
 {
-	int c = atomic_read(&mapping->i_mmap_writable);
-
-	/* Derived from the raw_atomic_inc_unless_negative() implementation. */
-	do {
-		if (c < 0)
-			return -EPERM;
-	} while (!__sync_bool_compare_and_swap(&mapping->i_mmap_writable, c, c+1));
-
-	return 0;
+	return atomic_inc_unless_negative(&mapping->i_mmap_writable) ?
+		0 : -EPERM;
 }
 
 static inline unsigned long move_page_tables(struct pagetable_move_control *pmc)

-- 
2.50.1