Some recent commits incorrectly assumed 4-byte alignment of locks.
That assumption fails on Linux/m68k (and, interestingly, would have
failed on Linux/cris also). The jump label implementation makes a
similar alignment assumption.
The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures.
But atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned
on m68k.
This patch brings a little uniformity by specifying natural alignment
for atomic types. One benefit is that atomic64_t variables do not get
split across a page boundary. The cost is that some structs grow which
leads to cache misses and wasted memory.
See also, commit bbf2a330d92c ("x86: atomic64: The atomic64_t data type
should be 8 bytes aligned on 32-bit too").
Cc: Guo Ren <[email protected]>
Cc: [email protected]
Cc: Geert Uytterhoeven <[email protected]>
Cc: [email protected]
Cc: Dinh Nguyen <[email protected]>
Cc: Jonas Bonn <[email protected]>
Cc: Stefan Kristiansson <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: [email protected]
Cc: Yoshinori Sato <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: John Paul Adrian Glaubitz <[email protected]>
Cc: [email protected]
Link:
https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7...@mail.gmail.com
Link:
https://lore.kernel.org/lkml/camuhmdw7ab13ddgs2acmqcix5objk0o2dg_fxzr8_g58rc1...@mail.gmail.com/
Acked-by: Guo Ren <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Finn Thain <[email protected]>
---
Changed since v5:
- Added tags from Guo Ren and Arnd Bergmann.
Changed since v2:
- Specify natural alignment for atomic64_t.
Changed since v1:
- atomic64_t now gets an __aligned attribute too.
- The 'Fixes' tag has been dropped because Lance sent a different fix
for commit e711faaafbe5 ("hung_task: replace blocker_mutex with encoded
blocker") that's suitable for -stable.
---
include/asm-generic/atomic64.h | 2 +-
include/linux/types.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h
index 100d24b02e52..f22ccfc0df98 100644
--- a/include/asm-generic/atomic64.h
+++ b/include/asm-generic/atomic64.h
@@ -10,7 +10,7 @@
#include <linux/types.h>
typedef struct {
- s64 counter;
+ s64 __aligned(sizeof(s64)) counter;
} atomic64_t;
#define ATOMIC64_INIT(i) { (i) }
diff --git a/include/linux/types.h b/include/linux/types.h
index d4437e9c452c..1760e1feeab9 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -180,7 +180,7 @@ typedef phys_addr_t resource_size_t;
typedef unsigned long irq_hw_number_t;
typedef struct {
- int counter;
+ int __aligned(sizeof(int)) counter;
} atomic_t;
#define ATOMIC_INIT(i) { (i) }
--
2.49.1
