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Subject: Re: [PATCH v4] fault-injection: introduce kvmalloc fallback options
To:     Mikulas Patocka <mpatocka@redhat.com>,
        Michal Hocko <mhocko@kernel.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        David Miller <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        eric.dumazet@gmail.com, edumazet@google.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        mst@redhat.com, jasowang@redhat.com,
        virtualization@lists.linux-foundation.org, dm-devel@redhat.com,
        Vlastimil Babka <vbabka@suse.cz>
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From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <1114eda5-9b1f-4db8-2090-556b4a37c532@infradead.org>
Date:   Wed, 25 Apr 2018 13:20:39 -0700
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On 04/25/2018 01:02 PM, Mikulas Patocka wrote:
> 
> 
> From: Mikulas Patocka <mpatocka@redhat.com>
> Subject: [PATCH v4] fault-injection: introduce kvmalloc fallback options
> 
> This patch introduces a fault-injection option "kvmalloc_fallback". This
> option makes kvmalloc randomly fall back to vmalloc.
> 
> Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then

  Unfortunately,

> uses DMA-API on the returned memory or frees it with kfree. Such bugs were
> found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific
> code. This options helps to test for these bugs.
> 
> The patch introduces a config option FAIL_KVMALLOC_FALLBACK_PROBABILITY.
> It can be enabled in distribution debug kernels, so that kvmalloc abuse
> can be tested by the users. The default can be overriden with

                                                 overridden

> "kvmalloc_fallback" parameter or in /sys/kernel/debug/kvmalloc_fallback/.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> 
> ---
>  Documentation/fault-injection/fault-injection.txt |    7 +++++
>  include/linux/fault-inject.h                      |    9 +++---
>  kernel/futex.c                                    |    2 -
>  lib/Kconfig.debug                                 |   15 +++++++++++
>  mm/failslab.c                                     |    2 -
>  mm/page_alloc.c                                   |    2 -
>  mm/util.c                                         |   30 ++++++++++++++++++++++
>  7 files changed, 60 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6/Documentation/fault-injection/fault-injection.txt
> ===================================================================
> --- linux-2.6.orig/Documentation/fault-injection/fault-injection.txt	2018-04-16 21:08:34.000000000 +0200
> +++ linux-2.6/Documentation/fault-injection/fault-injection.txt	2018-04-25 21:36:36.000000000 +0200
> @@ -15,6 +15,12 @@ o fail_page_alloc
>  
>    injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
>  
> +o kvmalloc_faillback

     kvmalloc_fallback

> +
> +  makes the function kvmalloc randonly fall back to vmalloc. This could be used

                                 randomly

> +  to detects bugs such as using DMA-API on the result of kvmalloc or freeing
> +  the result of kvmalloc with free.
> +
>  o fail_futex
>  
>    injects futex deadlock and uaddr fault errors.
> @@ -167,6 +173,7 @@ use the boot option:
>  
>  	failslab=
>  	fail_page_alloc=
> +	kvmalloc_faillback=

	kvmalloc_fallback=

>  	fail_make_request=
>  	fail_futex=
>  	mmc_core.fail_request=<interval>,<probability>,<space>,<times>

> Index: linux-2.6/lib/Kconfig.debug
> ===================================================================
> --- linux-2.6.orig/lib/Kconfig.debug	2018-04-25 15:56:16.000000000 +0200
> +++ linux-2.6/lib/Kconfig.debug	2018-04-25 21:39:45.000000000 +0200
> @@ -1527,6 +1527,21 @@ config FAIL_PAGE_ALLOC
>  	help
>  	  Provide fault-injection capability for alloc_pages().
>  
> +config FAIL_KVMALLOC_FALLBACK_PROBABILITY
> +	int "Default kvmalloc fallback probability"
> +	depends on FAULT_INJECTION
> +	range 0 100
> +	default "0"
> +	help
> +	  This option will make kvmalloc randomly fall back to vmalloc.
> +	  Normally, kvmalloc falls back to vmalloc only rarely, if memory
> +	  is fragmented.
> +
> +	  This option helps to detect hard-to-reproduce driver bugs, for
> +	  example using DMA API on the result of kvmalloc.
> +
> +	  The default may be overriden with the kvmalloc_faillback parameter.

	                     overridden         kvmalloc_fallback

> +
>  config FAIL_MAKE_REQUEST
>  	bool "Fault-injection capability for disk IO"
>  	depends on FAULT_INJECTION && BLOCK

-- 
~Randy