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Date:   Wed, 25 Apr 2018 14:18:42 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Mikulas Patocka <mpatocka@redhat.com>
cc:     Randy Dunlap <rdunlap@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        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>
Subject: Re: [PATCH v5] fault-injection: introduce kvmalloc fallback
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On Wed, 25 Apr 2018, Mikulas Patocka wrote:

> From: Mikulas Patocka <mpatocka@redhat.com>
> Subject: [PATCH] fault-injection: introduce kvmalloc fallback options
> 
> This patch introduces a fault-injection option "kvmalloc_fallback". This
> option makes kvmalloc randomly fall back to vmalloc.
> 
> Unfortunately, some kernel code has bugs - it uses kvmalloc and then
> 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 overridden with
> "kvmalloc_fallback" parameter or in /sys/kernel/debug/kvmalloc_fallback/.
> 

Do we really need the new config option?  This could just be manually 
tunable via fault injection IIUC.

> 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_fallback
> +
> +  makes the function kvmalloc randomly fall back to vmalloc. This could be used
> +  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_fallback=
>  	fail_make_request=
>  	fail_futex=
>  	mmc_core.fail_request=<interval>,<probability>,<space>,<times>
> Index: linux-2.6/include/linux/fault-inject.h
> ===================================================================
> --- linux-2.6.orig/include/linux/fault-inject.h	2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/include/linux/fault-inject.h	2018-04-25 21:38:22.000000000 +0200
> @@ -31,17 +31,18 @@ struct fault_attr {
>  	struct dentry *dname;
>  };
>  
> -#define FAULT_ATTR_INITIALIZER {					\
> +#define FAULT_ATTR_INITIALIZER(p) {					\
> +		.probability = (p),					\
>  		.interval = 1,						\
> -		.times = ATOMIC_INIT(1),				\
> +		.times = ATOMIC_INIT((p) ? -1 : 1),			\
> +		.verbose = (p) ? 0 : 2,					\
>  		.require_end = ULONG_MAX,				\
>  		.stacktrace_depth = 32,					\
>  		.ratelimit_state = RATELIMIT_STATE_INIT_DISABLED,	\
> -		.verbose = 2,						\
>  		.dname = NULL,						\
>  	}
>  
> -#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
> +#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER(0)
>  int setup_fault_attr(struct fault_attr *attr, char *str);
>  bool should_fail(struct fault_attr *attr, ssize_t size);
>  
> 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 overridden with the kvmalloc_fallback parameter.
> +
>  config FAIL_MAKE_REQUEST
>  	bool "Fault-injection capability for disk IO"
>  	depends on FAULT_INJECTION && BLOCK
> Index: linux-2.6/mm/util.c
> ===================================================================
> --- linux-2.6.orig/mm/util.c	2018-04-25 15:48:39.000000000 +0200
> +++ linux-2.6/mm/util.c	2018-04-25 21:43:31.000000000 +0200
> @@ -14,6 +14,7 @@
>  #include <linux/hugetlb.h>
>  #include <linux/vmalloc.h>
>  #include <linux/userfaultfd_k.h>
> +#include <linux/fault-inject.h>
>  
>  #include <asm/sections.h>
>  #include <linux/uaccess.h>
> @@ -377,6 +378,29 @@ unsigned long vm_mmap(struct file *file,
>  }
>  EXPORT_SYMBOL(vm_mmap);
>  
> +#ifdef CONFIG_FAULT_INJECTION
> +
> +static struct fault_attr kvmalloc_fallback =
> +	FAULT_ATTR_INITIALIZER(CONFIG_FAIL_KVMALLOC_FALLBACK_PROBABILITY);
> +
> +static int __init setup_kvmalloc_fallback(char *str)
> +{
> +	return setup_fault_attr(&kvmalloc_fallback, str);
> +}
> +
> +__setup("kvmalloc_fallback=", setup_kvmalloc_fallback);
> +
> +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> +static int __init kvmalloc_fallback_debugfs_init(void)
> +{
> +	fault_create_debugfs_attr("kvmalloc_fallback", NULL, &kvmalloc_fallback);
> +	return 0;
> +}
> +late_initcall(kvmalloc_fallback_debugfs_init);
> +#endif
> +
> +#endif
> +
>  /**
>   * kvmalloc_node - attempt to allocate physically contiguous memory, but upon
>   * failure, fall back to non-contiguous (vmalloc) allocation.
> @@ -404,6 +428,11 @@ void *kvmalloc_node(size_t size, gfp_t f
>  	 */
>  	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
>  
> +#ifdef CONFIG_FAULT_INJECTION
> +	if (should_fail(&kvmalloc_fallback, size))
> +		goto do_vmalloc;
> +#endif
> +
>  	/*
>  	 * We want to attempt a large physically contiguous block first because
>  	 * it is less likely to fragment multiple larger blocks and therefore
> @@ -427,6 +456,7 @@ void *kvmalloc_node(size_t size, gfp_t f
>  	if (ret || size <= PAGE_SIZE)
>  		return ret;
>  
> +do_vmalloc: __maybe_unused
>  	return __vmalloc_node_flags_caller(size, node, flags,
>  			__builtin_return_address(0));
>  }
> Index: linux-2.6/kernel/futex.c
> ===================================================================
> --- linux-2.6.orig/kernel/futex.c	2018-02-14 20:24:42.000000000 +0100
> +++ linux-2.6/kernel/futex.c	2018-04-25 21:11:33.000000000 +0200
> @@ -288,7 +288,7 @@ static struct {
>  
>  	bool ignore_private;
>  } fail_futex = {
> -	.attr = FAULT_ATTR_INITIALIZER,
> +	.attr = FAULT_ATTR_INITIALIZER(0),
>  	.ignore_private = false,
>  };
>  
> Index: linux-2.6/mm/failslab.c
> ===================================================================
> --- linux-2.6.orig/mm/failslab.c	2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/mm/failslab.c	2018-04-25 21:11:40.000000000 +0200
> @@ -9,7 +9,7 @@ static struct {
>  	bool ignore_gfp_reclaim;
>  	bool cache_filter;
>  } failslab = {
> -	.attr = FAULT_ATTR_INITIALIZER,
> +	.attr = FAULT_ATTR_INITIALIZER(0),
>  	.ignore_gfp_reclaim = true,
>  	.cache_filter = false,
>  };
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c	2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/mm/page_alloc.c	2018-04-25 21:11:47.000000000 +0200
> @@ -3055,7 +3055,7 @@ static struct {
>  	bool ignore_gfp_reclaim;
>  	u32 min_order;
>  } fail_page_alloc = {
> -	.attr = FAULT_ATTR_INITIALIZER,
> +	.attr = FAULT_ATTR_INITIALIZER(0),
>  	.ignore_gfp_reclaim = true,
>  	.ignore_gfp_highmem = true,
>  	.min_order = 1,
> 
>