[PATCH] Revert "lib/plist.c: enforce memory ordering in plist_check_list"

[Kuan-Wei Chiu <visitorckw@gmail.com>]

This reverts commit 7abcb84f953df037d40fad66f2109db318dd155b.

The introduction of WRITE_ONCE() calls for the 'prev' and 'next'
variables inside plist_check_list() was a misapplication. WRITE_ONCE()
is fundamentally a compiler barrier designed to prevent compiler
optimizations (like caching or reordering) on shared memory locations.
However, the variables 'prev' and 'next' are local, stack-allocated
pointers accessed only by the current thread's invocation of the
function.

Since these pointers are thread-local and are never accessed
concurrently, applying WRITE_ONCE() to them is semantically incorrect
and unnecessary. Furthermore, the use of WRITE_ONCE() on local
variables prevents the compiler from performing standard optimizations,
such as keeping these variables cached solely in CPU registers
throughout the loop, potentially introducing performance overhead.
Restore the conventional C assignment for local loop variables,
allowing the compiler to generate optimal code.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 lib/plist.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/plist.c b/lib/plist.c
index 330febb4bd7d..ba677c31e8f3 100644
--- a/lib/plist.c
+++ b/lib/plist.c
@@ -47,8 +47,8 @@ static void plist_check_list(struct list_head *top)
 
 	plist_check_prev_next(top, prev, next);
 	while (next != top) {
-		WRITE_ONCE(prev, next);
-		WRITE_ONCE(next, prev->next);
+		prev = next;
+		next = prev->next;
 		plist_check_prev_next(top, prev, next);
 	}
 }
-- 
2.52.0.rc1.455.g30608eb744-goog