scsi: hpsa: Add an assert to prevent __packed reintroduction

Link: https://lore.kernel.org/r/20210330071958.3788214-3-slyfox@gentoo.org
Fixes: f749d8b ("scsi: hpsa: Correct dev cmds outstanding for retried cmds")
CC: linux-ia64@vger.kernel.org
CC: storagedev@microchip.com
CC: linux-scsi@vger.kernel.org
CC: Joe Szczypek <jszczype@redhat.com>
CC: Scott Benesh <scott.benesh@microchip.com>
CC: Scott Teel <scott.teel@microchip.com>
CC: Tomas Henzl <thenzl@redhat.com>
CC: "Martin K. Petersen" <martin.petersen@oracle.com>
CC: Don Brace <don.brace@microchip.com>
Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Suggested-by: Don Brace <don.brace@microchip.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Sergei Trofimovich

drivers/scsi/hpsa_cmd.h

@@ -22,6 +22,9 @@
 
 #include <linux/compiler.h>
 
+#include <linux/build_bug.h> /* static_assert */
+#include <linux/stddef.h> /* offsetof */
+
 /* general boundary defintions */
 #define SENSEINFOBYTES          32 /* may vary between hbas */
 #define SG_ENTRIES_IN_CMD	32 /* Max SG entries excluding chain blocks */
@@ -454,6 +457,15 @@ struct CommandList {
 	atomic_t refcount; /* Must be last to avoid memset in hpsa_cmd_init() */
 } __aligned(COMMANDLIST_ALIGNMENT);
 
+/*
+ * Make sure our embedded atomic variable is aligned. Otherwise we break atomic
+ * operations on architectures that don't support unaligned atomics like IA64.
+ *
+ * The assert guards against reintroductin against unwanted __packed to
+ * the struct CommandList.
+ */
+static_assert(offsetof(struct CommandList, refcount) % __alignof__(atomic_t) == 0);
+
 /* Max S/G elements in I/O accelerator command */
 #define IOACCEL1_MAXSGENTRIES           24
 #define IOACCEL2_MAXSGENTRIES		28