Re: [PATCH] mm: make should_failslab always available for fault injection

[Howard McLauchlan <hmclauchlan@fb.com>]

On 02/21/2018 06:03 PM, Howard McLauchlan wrote:
> should_failslab() is a convenient function to hook into for directed
> error injection into kmalloc(). However, it is only available if a
> config flag is set.
> 
> The following BCC script, for example, fails kmalloc() calls after a
> btrfs umount:
> 
> from bcc import BPF
> 
> prog = r"""
> BPF_HASH(flag);
> 
> int kprobe__btrfs_close_devices(void *ctx) {
>         u64 key = 1;
>         flag.update(&key, &key);
>         return 0;
> }
> 
> int kprobe__should_failslab(struct pt_regs *ctx) {
>         u64 key = 1;
>         u64 *res;
>         res = flag.lookup(&key);
>         if (res != 0) {
>             bpf_override_return(ctx, -ENOMEM);
>         }
>         return 0;
> }
> """
> b = BPF(text=prog)
> 
> while 1:
>     b.kprobe_poll()
> 
> This patch refactors the should_failslab implementation so that the
> function is always available for error injection, independent of flags.
> 
> This change would be similar in nature to commit f5490d3ec921 ("block:
> Add should_fail_bio() for bpf error injection").
> 
> Signed-off-by: Howard McLauchlan <hmclauchlan@fb.com>
> ---
>  include/linux/fault-inject.h | 5 +++--
>  mm/failslab.c                | 2 +-
>  mm/slab_common.c             | 8 ++++++++
>  3 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
> index c3c95d18bf43..7e6c77740413 100644
> --- a/include/linux/fault-inject.h
> +++ b/include/linux/fault-inject.h
> @@ -64,10 +64,11 @@ static inline struct dentry *fault_create_debugfs_attr(const char *name,
>  
>  struct kmem_cache;
>  
> +int should_failslab(struct kmem_cache *s, gfp_t gfpflags);
>  #ifdef CONFIG_FAILSLAB
> -extern bool should_failslab(struct kmem_cache *s, gfp_t gfpflags);
> +extern bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags);
>  #else
> -static inline bool should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> +static inline bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
>  {
>  	return false;
>  }
> diff --git a/mm/failslab.c b/mm/failslab.c
> index 8087d976a809..1f2f248e3601 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -14,7 +14,7 @@ static struct {
>  	.cache_filter = false,
>  };
>  
> -bool should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> +bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
>  {
>  	/* No fault-injection for bootstrap cache */
>  	if (unlikely(s == kmem_cache))
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 10f127b2de7c..e99884490f14 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1532,3 +1532,11 @@ EXPORT_TRACEPOINT_SYMBOL(kmalloc_node);
>  EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc_node);
>  EXPORT_TRACEPOINT_SYMBOL(kfree);
>  EXPORT_TRACEPOINT_SYMBOL(kmem_cache_free);
> +
> +int should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> +{
> +	if (__should_failslab(s, gfpflags))
> +		return -ENOMEM;
> +	return 0;
> +}
> +ALLOW_ERROR_INJECTION(should_failslab, ERRNO);
> 
The script is missing a '#include <linux/mm.h>' on the first line of the C program text.  

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