Re: [PATCH] failslab: add ability to filter slab caches

From: David Rientjes
Date: Wed Feb 24 2010 - 16:21:17 EST

On Wed, 24 Feb 2010, Dmitry Monakhov wrote:

> >> Example:
> >> echo 1 > /sys/kernel/slab/skbuff_head_cache/failslab
> >> echo 1 > /sys/kernel/debug/failslab/cache-filter
> >>
> >
> > Where's the changelog?
> I've hoped than subject is enough. But if you want more verbose
> changelog, take following version.
>

Please do not attach patches to emails when sending to LKML, they are
preferred to be inline. See Documentation/SubmittingPatches.

> This patch allow to inject faults only for specific slabs.
> In order to preserve default behavior cache filter is off by
> default (all caches are faulty).
>
> One may define specific set of slabs like this:
> # mark skbuff_head_cache as faulty
> echo 1 > /sys/kernel/slab/skbuff_head_cache/failslab
> # Turn on cache filter (off by default)
> echo 1 > /sys/kernel/debug/failslab/cache-filter
> # Turn on fault injection
> echo 1 > /sys/kernel/debug/failslab/times
> echo 1 > /sys/kernel/debug/failslab/probability
>

Please describe your new slub_debug=a option here as well as in an update
to Documentation/vm/slub.txt.

> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> ---
> include/linux/fault-inject.h | 4 ++--
> include/linux/slab.h | 4 +++-
> mm/failslab.c | 18 +++++++++++++++---
> mm/slab.c | 2 +-
> mm/slub.c | 31 +++++++++++++++++++++++++++++--
> 5 files changed, 50 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
> index 06ca9b2..d935647 100644
> --- a/include/linux/fault-inject.h
> +++ b/include/linux/fault-inject.h
> @@ -82,9 +82,9 @@ static inline void cleanup_fault_attr_dentries(struct fault_attr *attr)
> #endif /* CONFIG_FAULT_INJECTION */
>
> #ifdef CONFIG_FAILSLAB
> -extern bool should_failslab(size_t size, gfp_t gfpflags);
> +extern bool should_failslab(size_t size, gfp_t gfpflags, unsigned long c_flags);
> #else
> -static inline bool should_failslab(size_t size, gfp_t gfpflags)
> +static inline bool should_failslab(size_t size, gfp_t gfpflags, unsigned long f)
> {
> return false;
> }

As I said in the first review, these need to be more descriptive: 'flags'
would be better.

> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 2da8372..9e03a81 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -70,7 +70,9 @@
> #else
> # define SLAB_NOTRACK 0x00000000UL
> #endif
> -
> +#ifdef CONFIG_FAILSLAB
> +# define SLAB_FAILSLAB 0x02000000UL /* Fault injection filter mark */
> +#endif

Trailing whitespace on your #endif.

> /* The following flags affect the page allocator grouping pages by mobility */
> #define SLAB_RECLAIM_ACCOUNT 0x00020000UL /* Objects are reclaimable */
> #define SLAB_TEMPORARY SLAB_RECLAIM_ACCOUNT /* Objects are short-lived */
> diff --git a/mm/failslab.c b/mm/failslab.c
> index 9339de5..bb41f98 100644
> --- a/mm/failslab.c
> +++ b/mm/failslab.c
> @@ -1,18 +1,22 @@
> #include <linux/fault-inject.h>
> #include <linux/gfp.h>
> +#include <linux/slab.h>
>
> static struct {
> struct fault_attr attr;
> u32 ignore_gfp_wait;
> + int cache_filter;
> #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> struct dentry *ignore_gfp_wait_file;
> + struct dentry *cache_filter_file;
> #endif
> } failslab = {
> .attr = FAULT_ATTR_INITIALIZER,
> .ignore_gfp_wait = 1,
> + .cache_filter = 0,
> };
>
> -bool should_failslab(size_t size, gfp_t gfpflags)
> +bool should_failslab(size_t size, gfp_t gfpflags, unsigned long cache_flags)
> {
> if (gfpflags & __GFP_NOFAIL)
> return false;
> @@ -20,6 +24,9 @@ bool should_failslab(size_t size, gfp_t gfpflags)
> if (failslab.ignore_gfp_wait && (gfpflags & __GFP_WAIT))
> return false;
>
> + if (failslab.cache_filter && !(cache_flags & SLAB_FAILSLAB))
> + return false;
> +
> return should_fail(&failslab.attr, size);
> }
>
> @@ -30,7 +37,6 @@ static int __init setup_failslab(char *str)
> __setup("failslab=", setup_failslab);
>
> #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> -
> static int __init failslab_debugfs_init(void)
> {
> mode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
> @@ -46,8 +52,14 @@ static int __init failslab_debugfs_init(void)
> debugfs_create_bool("ignore-gfp-wait", mode, dir,
> &failslab.ignore_gfp_wait);
>
> - if (!failslab.ignore_gfp_wait_file) {
> + failslab.cache_filter_file =
> + debugfs_create_bool("cache-filter", mode, dir,
> + &failslab.cache_filter);
> +
> + if (!failslab.ignore_gfp_wait_file ||
> + !failslab.cache_filter_file) {
> err = -ENOMEM;
> + debugfs_remove(failslab.cache_filter_file);
> debugfs_remove(failslab.ignore_gfp_wait_file);
> cleanup_fault_attr_dentries(&failslab.attr);
> }
> diff --git a/mm/slab.c b/mm/slab.c
> index 7451bda..33496b7 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3101,7 +3101,7 @@ static bool slab_should_failslab(struct kmem_cache *cachep, gfp_t flags)
> if (cachep == &cache_cache)
> return false;
>
> - return should_failslab(obj_size(cachep), flags);
> + return should_failslab(obj_size(cachep), flags, cachep->flags);
> }
>

cachep->flags for CONFIG_SLAB is of type unsigned int and
should_failslab() takes an unsigned long.

> static inline void *____cache_alloc(struct kmem_cache *cachep, gfp_t flags)
> diff --git a/mm/slub.c b/mm/slub.c
> index 8d71aaf..64114fa 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -151,7 +151,8 @@
> * Set of flags that will prevent slab merging
> */
> #define SLUB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
> - SLAB_TRACE | SLAB_DESTROY_BY_RCU | SLAB_NOLEAKTRACE)
> + SLAB_TRACE | SLAB_DESTROY_BY_RCU | SLAB_NOLEAKTRACE | \
> + SLAB_FAILSLAB)
>
> #define SLUB_MERGE_SAME (SLAB_DEBUG_FREE | SLAB_RECLAIM_ACCOUNT | \
> SLAB_CACHE_DMA | SLAB_NOTRACK)

As I mentioned in my first review of your patch, this breaks for
CONFIG_FAILSLAB=n. Please make sure your patch compiles for the
defconfig.
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