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Date:   Wed, 25 Apr 2018 17:22:27 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     David Rientjes <rientjes@google.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, David Rientjes wrote:

> 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.

We do, because we want to enable it in RHEL and Fedora debugging kernels, 
so that it will be tested by the users.

The users won't use some extra magic kernel options or debugfs files.

Mikulas


> > 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,
> > 
> > 
>