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Subject[PATCH v4] fault-injection: introduce kvmalloc fallback options


On Tue, 24 Apr 2018, Michal Hocko wrote:

> > > Wouldn't it be equally trivial to simply enable the fault injection? You
> > > would get additional failure paths testing as a bonus.
> >
> > The RHEL and Fedora debugging kernels are compiled with fault injection.
> > But the fault-injection framework will do nothing unless it is enabled by
> > a kernel parameter or debugfs write.
> >
> > Most users don't know about the fault injection kernel parameters or
> > debugfs files and won't enabled it. We need a CONFIG_ option to enable it
> > by default in the debugging kernels (and we could add a kernel parameter
> > to override the default, fine-tune the fallback probability etc.)
>
> If it is a real issue to install the debugging kernel with the required
> kernel parameter then I a config option for the default on makes sense
> to me.

Yes - the debug kernels use the same default kernel parameters as
non-debug kernels and it is expected that all debug features are enabled
by default.

Here I'm sending the patch using the fault-injection framework and the new
option CONFIG_FAIL_KVMALLOC_FALLBACK_PROBABILITY.

Mikulas



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
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
"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
+
+ makes the function kvmalloc randonly 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_faillback=
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 overriden with the kvmalloc_faillback 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,
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