linux-kernel - [PATCH v2 1/4] tools/include: Implement a couple of atomic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250828-b4-vma-no-atomic-h-v2-1-02d146a58ed2@google.com>
Date: Thu, 28 Aug 2025 12:27:58 +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 1/4] tools/include: Implement a couple of atomic_t ops

The VMA tests need an operation equivalent to
atomic_inc_unless_negative() to implement a fake mapping_map_writable().
Adding it will enable them to switch to the shared atomic headers and
simplify that fake implementation.

In order to add that, also add atomic_try_cmpxchg() which can be used to
implement it. This is copied from Documentation/atomic_t.txt. Then,
implement atomic_inc_unless_negative() itself based on the
raw_atomic_dec_unless_positive() in
include/linux/atomic/atomic-arch-fallback.h.

There's no present need for a highly-optimised version of this (nor any
reason to think this implementation is sub-optimal on x86) so just
implement this with generic C, no x86-specifics.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 tools/include/linux/atomic.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/include/linux/atomic.h b/tools/include/linux/atomic.h
index 01907b33537e04c5e860dd2cd61a61dfab6ea8f1..50c66ba9ada58cf05125e2e2472734bf3b0f8595 100644
--- a/tools/include/linux/atomic.h
+++ b/tools/include/linux/atomic.h
@@ -12,4 +12,26 @@ void atomic_long_set(atomic_long_t *v, long i);
 #define  atomic_cmpxchg_release         atomic_cmpxchg
 #endif /* atomic_cmpxchg_relaxed */

+static inline bool atomic_try_cmpxchg(atomic_t *ptr, int *oldp, int new)
+{
+	int ret, old = *oldp;
+
+	ret = atomic_cmpxchg(ptr, old, new);
+	if (ret != old)
+		*oldp = ret;
+	return ret == old;
+}
+
+static inline bool atomic_inc_unless_negative(atomic_t *v)
+{
+	int c = atomic_read(v);
+
+	do {
+		if (unlikely(c < 0))
+			return false;
+	} while (!atomic_try_cmpxchg(v, &c, c + 1));
+
+	return true;
+}
+
 #endif /* __TOOLS_LINUX_ATOMIC_H */

-- 
2.50.1