+ kcov-load-acquire-coverage-count-in-user-space-code.patch added to mm-nonmm-unstable branch

+ kcov-load-acquire-coverage-count-in-user-space-code.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: kcov: load acquire coverage count in user-space code
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     kcov-load-acquire-coverage-count-in-user-space-code.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kcov-load-acquire-coverage-count-in-user-space-code.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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------------------------------------------------------
From: Soham Bagchi <soham.bagchi@utah.edu>
Subject: kcov: load acquire coverage count in user-space code
Date: Mon, 28 Jul 2025 12:43:18 -0600

Updating the KCOV documentation to use a load-acquire
operation for the first element of the shared memory
buffer between kernel-space and user-space.

The load-acquire pairs with the write memory barrier
used in kcov_move_area()

Link: https://lkml.kernel.org/r/20250728184318.1839137-2-soham.bagchi@utah.edu
Signed-off-by: Soham Bagchi <soham.bagchi@utah.edu>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Macro Elver <elver@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/dev-tools/kcov.rst |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/Documentation/dev-tools/kcov.rst~kcov-load-acquire-coverage-count-in-user-space-code
+++ a/Documentation/dev-tools/kcov.rst
@@ -287,6 +287,11 @@ handle instance id.
 The following program demonstrates using KCOV to collect coverage from both
 local tasks spawned by the process and the global task that handles USB bus #1:
 
+The user-space code for KCOV should also use an acquire to fetch the count
+of coverage entries in the shared buffer. This acquire pairs with the
+corresponding write memory barrier (smp_wmb()) on the kernel-side in
+kcov_move_area().
+
 .. code-block:: c
 
     /* Same includes and defines as above. */
@@ -361,7 +366,7 @@ local tasks spawned by the process and t
 	 */
 	sleep(2);
 
-	n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
+	n = __atomic_load_n(&cover[0], __ATOMIC_ACQUIRE);
 	for (i = 0; i < n; i++)
 		printf("0x%lx\n", cover[i + 1]);
 	if (ioctl(fd, KCOV_DISABLE, 0))
_

Patches currently in -mm which might be from soham.bagchi@utah.edu are

kcov-use-write-memory-barrier-after-memcpy-in-kcov_move_area.patch
kcov-load-acquire-coverage-count-in-user-space-code.patch