Enforce that ipc_rcu_alloc returns a cacheline aligned pointer on SMP.
Rational:
The SysV sem code tries to move the main spinlock into a seperate cacheline
(____cacheline_aligned_in_smp). This works only if ipc_rcu_alloc returns
cacheline aligned pointers.
vmalloc and kmalloc return cacheline algined pointers, the implementation
of ipc_rcu_alloc breaks that.
Andrew: Could you merge it into -akpm and then forward it towards Linus' tree?
Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
---
ipc/util.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/ipc/util.c b/ipc/util.c
index 809ec5e..9623c8e 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -469,9 +469,7 @@ void ipc_free(void* ptr, int size)
struct ipc_rcu {
struct rcu_head rcu;
atomic_t refcount;
- /* "void *" makes sure alignment of following data is sane. */
- void *data[0];
-};
+} ____cacheline_aligned_in_smp;
/**
* ipc_rcu_alloc - allocate ipc and rcu space
@@ -489,12 +487,14 @@ void *ipc_rcu_alloc(int size)
if (unlikely(!out))
return NULL;
atomic_set(&out->refcount, 1);
- return out->data;
+ return out+1;
}
int ipc_rcu_getref(void *ptr)
{
- return atomic_inc_not_zero(&container_of(ptr, struct ipc_rcu,
data)->refcount);
+ struct ipc_rcu *p = ((struct ipc_rcu*)ptr)-1;
+
+ return atomic_inc_not_zero(&p->refcount);
}
/**
@@ -508,7 +508,7 @@ static void ipc_schedule_free(struct rcu_head *head)
void ipc_rcu_putref(void *ptr)
{
- struct ipc_rcu *p = container_of(ptr, struct ipc_rcu, data);
+ struct ipc_rcu *p = ((struct ipc_rcu*)ptr)-1;
if (!atomic_dec_and_test(&p->refcount))
return;
--
1.8.1.4
--
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