summaryrefslogtreecommitdiff
path: root/include
diff options
context:
space:
mode:
authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2015-11-05 18:44:18 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-11-05 19:34:48 -0800
commit720abae3d68ae966044497dd9ee5ccf3b16e700c (patch)
tree064c32bb272fa9914d4f844ce6fc183f1fcabeae /include
parent262d8a8779e24596ec3452ebb7d0a989de91089a (diff)
rcu: force alignment on struct callback_head/rcu_head
Make struct callback_head aligned to size of pointer. On most architectures it happens naturally due ABI requirements, but some architectures (like CRIS) have weird ABI and we need to ask it explicitly. The alignment is required to guarantee that bits 0 and 1 of @next will be clear under normal conditions -- as long as we use call_rcu(), call_rcu_bh(), call_rcu_sched(), or call_srcu() to queue callback. This guarantee is important for few reasons: - future call_rcu_lazy() will make use of lower bits in the pointer; - the structure shares storage spacer in struct page with @compound_head, which encode PageTail() in bit 0. The guarantee is needed to avoid false-positive PageTail(). False postive PageTail() caused crash on crisv32[1]. It happend due misaligned task_struct->rcu, which was byte-aligned. [1] http://lkml.kernel.org/r/55FAEA67.9000102@roeck-us.net Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Guenter Roeck <linux@roeck-us.net> Tested-by: Guenter Roeck <linux@roeck-us.net> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Mikael Starvik <starvik@axis.com> Cc: Jesper Nilsson <jesper.nilsson@axis.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/types.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/include/linux/types.h b/include/linux/types.h
index c314989d9158..70d8500bddf1 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -205,11 +205,25 @@ struct ustat {
* struct callback_head - callback structure for use with RCU and task_work
* @next: next update requests in a list
* @func: actual update function to call after the grace period.
+ *
+ * The struct is aligned to size of pointer. On most architectures it happens
+ * naturally due ABI requirements, but some architectures (like CRIS) have
+ * weird ABI and we need to ask it explicitly.
+ *
+ * The alignment is required to guarantee that bits 0 and 1 of @next will be
+ * clear under normal conditions -- as long as we use call_rcu(),
+ * call_rcu_bh(), call_rcu_sched(), or call_srcu() to queue callback.
+ *
+ * This guarantee is important for few reasons:
+ * - future call_rcu_lazy() will make use of lower bits in the pointer;
+ * - the structure shares storage spacer in struct page with @compound_head,
+ * which encode PageTail() in bit 0. The guarantee is needed to avoid
+ * false-positive PageTail().
*/
struct callback_head {
struct callback_head *next;
void (*func)(struct callback_head *head);
-};
+} __attribute__((aligned(sizeof(void *))));
#define rcu_head callback_head
typedef void (*rcu_callback_t)(struct rcu_head *head);