devres: Align data[] to ARCH_KMALLOC_MINALIGN

Initially we bumped into problem with 32-bit aligned atomic64_t
on ARC, see [1]. And then during quite lengthly discussion Peter Z.
mentioned ARCH_KMALLOC_MINALIGN which IMHO makes perfect sense.
If allocation is done by plain kmalloc() obtained buffer will be
ARCH_KMALLOC_MINALIGN aligned and then why buffer obtained via
devm_kmalloc() should have any other alignment?

This way we at least get the same behavior for both types of
allocation.

[1] http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004009.html
[2] http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004036.html

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: David Laight <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Greg KH <[email protected]>
Cc: <[email protected]> # 4.8+
Signed-off-by: Greg Kroah-Hartman <[email protected]>

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index 4aaf00d2098b432f6056cc2391621ccb2d78a1dc..e038e2b3b7ea4a7d53d2d7c189f9dbac269ea228 100644 (file)
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -26,8 +26,14 @@ struct devres_node {
 
 struct devres {
        struct devres_node              node;
-       /* -- 3 pointers */
-       unsigned long long              data[]; /* guarantee ull alignment */
+       /*
+        * Some archs want to perform DMA into kmalloc caches
+        * and need a guaranteed alignment larger than
+        * the alignment of a 64-bit integer.
+        * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same
+        * buffer alignment as if it was allocated by plain kmalloc().
+        */
+       u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
 };
 
 struct devres_group {