[PATCH v2] devres: Really align data field to unsigned long long

Alexey Brodkin
2018-07-08T17:58:50Z

Depending on ABI "long long" type of a particular 32-bit CPU
might be aligned by either word (32-bits) or double word (64-bits).
Make sure "data" is really 64-bit aligned for any 32-bit CPU.

At least for 32-bit ARC cores ABI requires "long long" types
to be aligned by normal 32-bit word. This makes "data" field aligned to
12 bytes. Which is still OK as long as we use 32-bit data only.

But once we want to use native atomic64_t type (i.e. when we use special
instructions LLOCKD/SCONDD for accessing 64-bit data) we easily hit
misaligned access exception.

That's because even on CPUs capable of non-aligned data access LL/SC
instructions require strict alignment.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
---

Changes v1 -> v2:

* Reworded commit message
* Inserted comment right in source [Thomas]

drivers/base/devres.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index f98a097e73f2..466fa59c866a 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -24,8 +24,12 @@ struct devres_node {

struct devres {
struct devres_node node;
- /* -- 3 pointers */
- unsigned long long data[]; /* guarantee ull alignment */
+ /*
+ * Depending on ABI "long long" type of a particular 32-bit CPU
+ * might be aligned by either word (32-bits) or double word (64-bits).
+ * Make sure "data" is really 64-bit aligned for any 32-bit CPU.
+ */
+ unsigned long long data[] __aligned(sizeof(unsigned long long));
};

struct devres_group {
--
2.17.1