[PATCH v4 3/3] mm: Pair atomic_set_release() with _read_acquire()

[Linus Walleij]

The code for syncing vmalloc memory PGD pointers is using
atomic_read() in pair with atomic_set_release() but the
proper pairing is atomic_read_acquire() paired with
atomic_set_release().

This is done to clearly instruct the compiler to not
reorder the memcpy() or similar calls inside the section
so that we do not observe changes to init_mm. memcpy()
calls should be identified by the compiler as having
unpredictable side effects, but let's try to be on the
safe side.

Cc: stable at vger.kernel.org
Fixes: d31e23aff011 ("ARM: mm: make vmalloc_seq handling SMP safe")
Suggested-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
 arch/arm/mm/ioremap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
index ff555823cceb..89f1c97f3079 100644
--- a/arch/arm/mm/ioremap.c
+++ b/arch/arm/mm/ioremap.c
@@ -141,7 +141,7 @@ void __check_vmalloc_seq(struct mm_struct *mm)
 	int seq;
 
 	do {
-		seq = atomic_read(&init_mm.context.vmalloc_seq);
+		seq = atomic_read_acquire(&init_mm.context.vmalloc_seq);
 		memcpy_pgd(mm, VMALLOC_START, VMALLOC_END);
 		if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) {
 			unsigned long start =

-- 
2.46.2