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Subject[ 41/69] ipc/util.c, ipc_rcu_alloc: cacheline align allocation
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Manfred Spraul <manfred@colorfullife.com>

commit 196aa0132fc7261f34b10ae1bfb44abc1bc69b3c upstream.

Enforce that ipc_rcu_alloc returns a cacheline aligned pointer on SMP.

Rationale:

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.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
ipc/util.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/ipc/util.c
+++ b/ipc/util.c
@@ -468,9 +468,7 @@ 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
@@ -488,12 +486,14 @@ 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);
}

/**
@@ -507,7 +507,7 @@ static void ipc_schedule_free(struct rcu

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;



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