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Commit f6a61680 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Paul Mackerras
Browse files

[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: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 8c9843e5

arch/powerpc/kernel/process.c

+31 −0
Original line number Diff line number Diff line
@@ -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 */

include/asm-powerpc/thread_info.h

+2 −6
Original line number Diff line number Diff line
@@ -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 */