On Tue, Dec 08, 2015 at 05:18:32PM +0100, Jesper Dangaard Brouer wrote:
> Move slab_should_failslab() check from SLAB allocator to generic
> slab_pre_alloc_hook(). The check guards against slab alloc
> fault-injects failures for the bootstrap slab that is used for
> allocating "kmem_cache" objects to the allocator itself.
>
> I'm not really happy with this code...
> ---
> mm/failslab.c | 2 ++
> mm/slab.c | 8 --------
> mm/slab.h | 23 ++++++++++++++++++++++-
> 3 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/mm/failslab.c b/mm/failslab.c
> index 79171b4a5826..a2ad28ba696c 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -13,6 +13,8 @@ static struct {
>
> bool should_failslab(size_t size, gfp_t gfpflags, unsigned long cache_flags)
> {
> + // Should we place bootstrap kmem_cache check here???
> +
> if (gfpflags & __GFP_NOFAIL)
> return false;
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 4765c97ce690..4684c2496982 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2917,14 +2917,6 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
> #define cache_alloc_debugcheck_after(a,b,objp,d) (objp)
> #endif
>
> -static bool slab_should_failslab(struct kmem_cache *cachep, gfp_t flags)
> -{
> - if (unlikely(cachep == kmem_cache))
> - return false;
> -
> - return should_failslab(cachep->object_size, flags, cachep->flags);
> -}
> -
> static inline void *____cache_alloc(struct kmem_cache *cachep, gfp_t flags)
> {
> void *objp;
> diff --git a/mm/slab.h b/mm/slab.h
> index 588bc5281fc8..4e7b0e62f3f4 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -360,6 +360,27 @@ static inline size_t slab_ksize(const struct kmem_cache *s)
> }
> #endif
>
> +/* FIXME: This construct sucks, because this compare+branch needs to
> + * get removed by compiler then !CONFIG_FAILSLAB (maybe compiler is
> + * smart enough to realize only "false" can be generated).
> + *
> + * Comments please: Pulling out CONFIG_FAILSLAB here looks ugly...
> + * should we instead change API of should_failslab() ??
> + *
> + * Next question: is the bootstrap cache check okay to add for all
> + * allocators? (this would be the easiest, else need more ugly ifdef's)
> + */
> +static inline bool slab_should_failslab(struct kmem_cache *cachep, gfp_t flags)
> +{
> + /* No fault-injection for bootstrap cache */
> +#ifdef CONFIG_FAILSLAB
> + if (unlikely(cachep == kmem_cache))
> + return false;
> +#endif
> +
> + return should_failslab(cachep->object_size, flags, cachep->flags);
> +}
> +
> static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
> gfp_t flags)
> {
> @@ -367,7 +388,7 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
> lockdep_trace_alloc(flags);
> might_sleep_if(gfpflags_allow_blocking(flags));
>
> - if (should_failslab(s->object_size, flags, s->flags))
> + if (slab_should_failslab(s, flags))
> return NULL;
It'd be better to remove slab_should_failslab() and insert following code
snippet here.
if (IS_ENABLED(CONFIG_FAILSLAB) &&
cachep != kmem_cache &&
should_failslab())
return NULL;
Thanks.
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