Re: [PATCH 2/3] slab,slub: don't enable interrupts during early boot

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2009-06-12 at 18:41 +0300, Pekka J Enberg wrote:
> From: Pekka Enberg <penberg@cs.helsinki.fi>
> 
> As explained by Benjamin Herrenschmidt:
> 
>   Oh and btw, your patch alone doesn't fix powerpc, because it's missing
>   a whole bunch of GFP_KERNEL's in the arch code... You would have to
>   grep the entire kernel for things that check slab_is_available() and
>   even then you'll be missing some.
> 
>   For example, slab_is_available() didn't always exist, and so in the
>   early days on powerpc, we used a mem_init_done global that is set form
>   mem_init() (not perfect but works in practice). And we still have code
>   using that to do the test.
> 
> Therefore, mask out __GFP_WAIT in the slab allocators in early boot code to
> avoid enabling interrupts.

Ack. I would also like to see that pushed down to page_alloc.c but
that's another discussion at this stage :-) (suspend/resume will need
that if we start using the mechanism to mask out FS and IO).

Cheers,
Ben.

> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
> ---
>  include/linux/gfp.h      |    3 +++
>  include/linux/slab.h     |    2 ++
>  include/linux/slob_def.h |    5 +++++
>  include/linux/slub_def.h |    2 ++
>  init/main.c              |    1 +
>  mm/slab.c                |   22 ++++++++++++++++++++++
>  mm/slub.c                |   16 ++++++++++++++++
>  7 files changed, 51 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 0bbc15f..ec0fede 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -85,6 +85,9 @@ struct vm_area_struct;
>  			__GFP_NOWARN|__GFP_REPEAT|__GFP_NOFAIL|\
>  			__GFP_NORETRY|__GFP_NOMEMALLOC)
>  
> +/* Control slab gfp mask during early boot */
> +#define SLAB_GFP_BOOT_MASK __GFP_BITS_MASK & ~(__GFP_WAIT|__GFP_IO|__GFP_FS);
> +
>  /* Control allocation constraints */
>  #define GFP_CONSTRAINT_MASK (__GFP_HARDWALL|__GFP_THISNODE)
>  
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 4880306..219b8fb 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -319,4 +319,6 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)
>  	return kmalloc_node(size, flags | __GFP_ZERO, node);
>  }
>  
> +void __init kmem_cache_init_late(void);
> +
>  #endif	/* _LINUX_SLAB_H */
> diff --git a/include/linux/slob_def.h b/include/linux/slob_def.h
> index 0ec00b3..bb5368d 100644
> --- a/include/linux/slob_def.h
> +++ b/include/linux/slob_def.h
> @@ -34,4 +34,9 @@ static __always_inline void *__kmalloc(size_t size, gfp_t flags)
>  	return kmalloc(size, flags);
>  }
>  
> +static inline void kmem_cache_init_late(void)
> +{
> +	/* Nothing to do */
> +}
> +
>  #endif /* __LINUX_SLOB_DEF_H */
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index be5d40c..4dcbc2c 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -302,4 +302,6 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
>  }
>  #endif
>  
> +void __init kmem_cache_init_late(void);
> +
>  #endif /* _LINUX_SLUB_DEF_H */
> diff --git a/init/main.c b/init/main.c
> index b3e8f14..f6204f7 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -640,6 +640,7 @@ asmlinkage void __init start_kernel(void)
>  				 "enabled early\n");
>  	early_boot_irqs_on();
>  	local_irq_enable();
> +	kmem_cache_init_late();
>  
>  	/*
>  	 * HACK ALERT! This is early. We're enabling the console before
> diff --git a/mm/slab.c b/mm/slab.c
> index cd76964..6c0c4df 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -304,6 +304,12 @@ struct kmem_list3 {
>  };
>  
>  /*
> + * The slab allocator is initialized with interrupts disabled. Therefore, make
> + * sure early boot allocations don't accidentally enable interrupts.
> + */
> +static gfp_t slab_gfp_mask __read_mostly = SLAB_GFP_BOOT_MASK;
> +
> +/*
>   * Need this for bootstrapping a per node allocator.
>   */
>  #define NUM_INIT_LISTS (3 * MAX_NUMNODES)
> @@ -1654,6 +1660,14 @@ void __init kmem_cache_init(void)
>  	 */
>  }
>  
> +void __init kmem_cache_init_late(void)
> +{
> +	/*
> +	 * Interrupts are enabled now so all GFP allocations are safe.
> +	 */
> +	slab_gfp_mask = __GFP_BITS_MASK;
> +}
> +
>  static int __init cpucache_init(void)
>  {
>  	int cpu;
> @@ -3237,6 +3251,10 @@ retry:
>  	}
>  
>  	if (!obj) {
> +		/* Lets avoid crashing in early boot code. */
> +		if (WARN_ON_ONCE((local_flags & ~slab_gfp_mask) != 0))
> +			local_flags &= slab_gfp_mask;
> +
>  		/*
>  		 * This allocation will be performed within the constraints
>  		 * of the current cpuset / memory policy requirements.
> @@ -3354,6 +3372,8 @@ __cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
>  	unsigned long save_flags;
>  	void *ptr;
>  
> +	flags &= slab_gfp_mask;
> +
>  	lockdep_trace_alloc(flags);
>  
>  	if (slab_should_failslab(cachep, flags))
> @@ -3434,6 +3454,8 @@ __cache_alloc(struct kmem_cache *cachep, gfp_t flags, void *caller)
>  	unsigned long save_flags;
>  	void *objp;
>  
> +	flags &= slab_gfp_mask;
> +
>  	lockdep_trace_alloc(flags);
>  
>  	if (slab_should_failslab(cachep, flags))
> diff --git a/mm/slub.c b/mm/slub.c
> index 3964d3c..30354bf 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -178,6 +178,12 @@ static enum {
>  	SYSFS		/* Sysfs up */
>  } slab_state = DOWN;
>  
> +/*
> + * The slab allocator is initialized with interrupts disabled. Therefore, make
> + * sure early boot allocations don't accidentally enable interrupts.
> + */
> +static gfp_t slab_gfp_mask __read_mostly = SLAB_GFP_BOOT_MASK;
> +
>  /* A list of all slab caches on the system */
>  static DECLARE_RWSEM(slub_lock);
>  static LIST_HEAD(slab_caches);
> @@ -1595,6 +1601,8 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
>  	unsigned long flags;
>  	unsigned int objsize;
>  
> +	gfpflags &= slab_gfp_mask;
> +
>  	lockdep_trace_alloc(gfpflags);
>  	might_sleep_if(gfpflags & __GFP_WAIT);
>  
> @@ -3104,6 +3112,14 @@ void __init kmem_cache_init(void)
>  		nr_cpu_ids, nr_node_ids);
>  }
>  
> +void __init kmem_cache_init_late(void)
> +{
> +	/*
> +	 * Interrupts are enabled now so all GFP allocations are safe.
> +	 */
> +	slab_gfp_mask = __GFP_BITS_MASK;
> +}
> +
>  /*
>   * Find a mergeable slab cache
>   */