[POWERPC] Fix kernel stack allocation alignment

The powerpc kernel stacks need to be naturally aligned, as they
contain the thread info at the bottom, which is obtained by
clearing the low bits of the stack pointer.

However, when using 64K pages, the stack is smaller than a page,
so we use kmalloc to allocate it, but that doesn't provide the
alignment guarantee we need.

It appeared to work so far... until one enables SLUB debugging
which then returns unaligned pointers.  Ooops...

This fixes it by using a slab cache with enforced alignment.  It
relies on my previous patch that adds a thread_info_cache_init()
callback.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 703100d5e4589c4e1f7566d0b720e05c560bf07d..6caad17ea72e6b0159461a84023c28ab454c637f 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1033,3 +1033,34 @@ void ppc64_runlatch_off(void)
        }
 }
 #endif
+
+#if THREAD_SHIFT < PAGE_SHIFT
+
+static struct kmem_cache *thread_info_cache;
+
+struct thread_info *alloc_thread_info(struct task_struct *tsk)
+{
+       struct thread_info *ti;
+
+       ti = kmem_cache_alloc(thread_info_cache, GFP_KERNEL);
+       if (unlikely(ti == NULL))
+               return NULL;
+#ifdef CONFIG_DEBUG_STACK_USAGE
+       memset(ti, 0, THREAD_SIZE);
+#endif
+       return ti;
+}
+
+void free_thread_info(struct thread_info *ti)
+{
+       kmem_cache_free(thread_info_cache, ti);
+}
+
+void thread_info_cache_init(void)
+{
+       thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
+                                             THREAD_SIZE, 0, NULL);
+       BUG_ON(thread_info_cache == NULL);
+}
+
+#endif /* THREAD_SHIFT < PAGE_SHIFT */

diff --git a/include/asm-powerpc/thread_info.h b/include/asm-powerpc/thread_info.h
index 40d5f98c44fca2f79fbdae31feb791bfff247bdc..d030f5ce39adafdac57aa0fd93d88bc8f985b2ea 100644 (file)
--- a/include/asm-powerpc/thread_info.h
+++ b/include/asm-powerpc/thread_info.h
@@ -80,12 +80,8 @@ struct thread_info {
 
 #else /* THREAD_SHIFT < PAGE_SHIFT */
 
-#ifdef CONFIG_DEBUG_STACK_USAGE
-#define alloc_thread_info(tsk) kzalloc(THREAD_SIZE, GFP_KERNEL)
-#else
-#define alloc_thread_info(tsk) kmalloc(THREAD_SIZE, GFP_KERNEL)
-#endif
-#define free_thread_info(ti)   kfree(ti)
+extern struct thread_info *alloc_thread_info(struct task_struct *tsk);
+extern void free_thread_info(struct thread_info *ti);
 
 #endif /* THREAD_SHIFT < PAGE_SHIFT */