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Subject[PATCH 2/2 -mm] fault-injection: lightweight code-coverage maximizer
From
Date
Allow all non-unique call stacks, as judged by pushed sequence of EIPs,
to be to be ignored as failure candidates.

Upon keying in
echo 1 >probability
echo 3 >verbose
echo -1 >times
a few dozen stacks are printk'ed, then system responsiveness
recovers to normal. Similarly, starting a non-trivial program
will print a few stacks before responsiveness recovers.

Intent is to make code-coverage-maximizing test lightweight, perhaps
light enough to remain enabled during the course of the developer's
interactive testing of new code.

Enabled by default. (/debug/fail*/stacktrace-depth > 0)

Signed-off-by: Don Mullis <dwm@meer.net>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
---
Documentation/fault-injection/fault-injection.txt | 7 +
include/linux/fault-inject.h | 4
lib/fault-inject.c | 123 +++++++++++++++++++---
3 files changed, 120 insertions(+), 14 deletions(-)

Index: linux-2.6.18/include/linux/fault-inject.h
===================================================================
--- linux-2.6.18.orig/include/linux/fault-inject.h
+++ linux-2.6.18/include/linux/fault-inject.h
@@ -23,6 +23,8 @@ struct fault_attr {
unsigned long require_end;
unsigned long reject_start;
unsigned long reject_end;
+ unsigned long uniquestack_depth;
+ atomic_t uniquestack_hash_table[256];

unsigned long count;

@@ -42,6 +44,7 @@ struct fault_attr {
struct dentry *require_end_file;
struct dentry *reject_start_file;
struct dentry *reject_end_file;
+ struct dentry *uniquestack_depth_file;
} dentries;

#endif
@@ -53,6 +56,7 @@ struct fault_attr {
.require_end = ULONG_MAX, \
.stacktrace_depth = 32, \
.verbose = 2, \
+ .uniquestack_depth = 32, \
}

#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
Index: linux-2.6.18/lib/fault-inject.c
===================================================================
--- linux-2.6.18.orig/lib/fault-inject.c
+++ linux-2.6.18/lib/fault-inject.c
@@ -1,3 +1,4 @@
+
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/random.h>
@@ -9,8 +10,12 @@
#include <linux/unwind.h>
#include <linux/stacktrace.h>
#include <linux/kallsyms.h>
+#include <linux/jhash.h>
+#include <linux/syscalls.h>
#include <linux/fault-inject.h>

+#define MAX_STACK_TRACE_DEPTH 32
+
/*
* setup_fault_attr() is a helper function for various __setup handlers, so it
* returns 0 on error, because that is what __setup handlers do.
@@ -21,10 +26,11 @@ int __init setup_fault_attr(struct fault
unsigned long interval;
int times;
int space;
+ unsigned long uniquestack_depth;

- /* "<interval>,<probability>,<space>,<times>" */
- if (sscanf(str, "%lu,%lu,%d,%d",
- &interval, &probability, &space, &times) < 4) {
+ /* "<interval>,<probability>,<space>,<times>,<uniquestack_depth>" */
+ if (sscanf(str, "%lu,%lu,%d,%d,%lu", &interval,
+ &probability, &space, &times, &uniquestack_depth) < 5) {
printk(KERN_WARNING
"FAULT_INJECTION: failed to parse arguments\n");
return 0;
@@ -34,6 +40,8 @@ int __init setup_fault_attr(struct fault
attr->interval = interval;
atomic_set(&attr->times, times);
atomic_set(&attr->space, space);
+ attr->uniquestack_depth = (uniquestack_depth <= MAX_STACK_TRACE_DEPTH) ?
+ uniquestack_depth : MAX_STACK_TRACE_DEPTH;

return 1;
}
@@ -53,8 +61,6 @@ static bool fail_task(struct fault_attr
return !in_interrupt() && task->make_it_fail;
}

-#define MAX_STACK_TRACE_DEPTH 32
-
#ifdef CONFIG_STACK_UNWIND

static asmlinkage int fail_stacktrace_callback(struct unwind_frame_info *info,
@@ -85,26 +91,54 @@ static bool fail_stacktrace(struct fault
return unwind_init_running(&info, fail_stacktrace_callback, attr);
}

+static asmlinkage int unique_stack_callback(struct unwind_frame_info *info,
+ void *arg)
+{
+ u32 entries[MAX_STACK_TRACE_DEPTH];
+ int depth;
+ struct fault_attr *attr = arg;
+
+ for (depth = 0; depth < attr->uniquestack_depth
+ && unwind(info) == 0 && UNW_PC(info); depth++) {
+ if (arch_unw_user_mode(info))
+ break;
+ }
+ if (attr->verbose > 8)
+ printk("%s: depth=%d, jhash=%x\n",
+ __FUNCTION__, depth,
+ jhash( entries, depth*sizeof(entries[0]), 0));
+ return jhash( entries, depth*sizeof(entries[0]), 0/*initval*/);
+}
+
+static int unique_stack_p(struct fault_attr *attr)
+{
+ struct unwind_frame_info info;
+
+ return unwind_init_running(&info, unique_stack_callback, attr);
+}
+
#elif defined(CONFIG_STACKTRACE)

+static void stack_trace(struct stack_trace *trace, int depth)
+{
+ trace->nr_entries = 0;
+ trace->max_entries = depth;
+ trace->skip = 1;
+ trace->all_contexts = 0;
+
+ save_stack_trace(trace, NULL);
+}
+
static bool fail_stacktrace(struct fault_attr *attr)
{
struct stack_trace trace;
- int depth = attr->stacktrace_depth;
unsigned long entries[MAX_STACK_TRACE_DEPTH];
int n;
bool found = (attr->require_start == 0 && attr->require_end == ULONG_MAX);

- if (depth == 0)
- return found;
-
- trace.nr_entries = 0;
trace.entries = entries;
- trace.max_entries = depth;
- trace.skip = 1;
- trace.all_contexts = 0;

- save_stack_trace(&trace, NULL);
+ stack_trace(&trace, attr->stacktrace_depth);
for (n = 0; n < trace.nr_entries; n++) {
if (attr->reject_start <= entries[n] &&
entries[n] < attr->reject_end)
@@ -116,6 +150,23 @@ static bool fail_stacktrace(struct fault
return found;
}

+static int unique_stack_p(struct fault_attr *attr)
+{
+ struct stack_trace trace;
+ unsigned long entries[MAX_STACK_TRACE_DEPTH];
+
+ trace.entries = entries;
+ stack_trace(&trace, attr->uniquestack_depth);
+
+ if (attr->verbose > 8)
+ printk("%s: trace.nr_entries=%d jhash=%x\n",
+ __FUNCTION__, trace.nr_entries,
+ jhash( trace.entries,
+ trace.nr_entries*sizeof(trace.entries[0]), 0));
+ return jhash( trace.entries,
+ trace.nr_entries*sizeof(trace.entries[0]), 0/*initval*/);
+}
+
#else

static inline bool fail_stacktrace(struct fault_attr *attr)
@@ -130,8 +181,42 @@ static inline bool fail_stacktrace(struc
return false;
}

+static int unique_stack_p(struct fault_attr *attr)
+{
+ (void) fail_stacktrace(attr);
+ return 0;
+}
#endif

+static bool fail_uniquestack(struct fault_attr *attr)
+{
+ u32 oldhash;
+ u32 newhash;
+ uint offset = 0;
+
+ newhash = unique_stack_p(attr);
+
+ for ( oldhash = newhash; oldhash != 0; offset++) {
+ oldhash = atomic_xchg(
+ &attr->uniquestack_hash_table[
+ (newhash+offset)%ARRAY_SIZE(attr->uniquestack_hash_table)],
+ oldhash);
+ if (oldhash == newhash)
+ return false;
+ if (offset >= ARRAY_SIZE(attr->uniquestack_hash_table)) {
+ printk(KERN_NOTICE
+ "FAULT_INJECTION: table overflow -- "
+ "fault injection disabled\n");
+ return false;
+ }
+ }
+
+ if (attr->verbose > 8)
+ printk(KERN_NOTICE "FAULT_INJECTION: newhash=%x offset==%d\n",
+ newhash, offset-1);
+ return true;
+}
+
/*
* This code is stolen from failmalloc-1.0
* http://www.nongnu.org/failmalloc/
@@ -162,6 +247,9 @@ bool should_fail(struct fault_attr *attr
if (!fail_stacktrace(attr))
return false;

+ if (!fail_uniquestack(attr))
+ return false;
+
fail_dump(attr);

if (atomic_read(&attr->times) != -1)
@@ -262,6 +350,9 @@ void cleanup_fault_attr_dentries(struct
debugfs_remove(attr->dentries.reject_end_file);
attr->dentries.reject_end_file = NULL;

+ debugfs_remove(attr->dentries.uniquestack_depth_file);
+ attr->dentries.uniquestack_depth_file = NULL;
+
if (attr->dentries.dir)
WARN_ON(!simple_empty(attr->dentries.dir));

@@ -315,6 +406,9 @@ int init_fault_attr_dentries(struct faul
attr->dentries.reject_end_file =
debugfs_create_ul("reject-end", mode, dir, &attr->reject_end);

+ attr->dentries.uniquestack_depth_file =
+ debugfs_create_ul_MAX_STACK_TRACE_DEPTH(
+ "uniquestack-depth", mode, dir, &attr->uniquestack_depth);

if (!attr->dentries.probability_file || !attr->dentries.interval_file
|| !attr->dentries.times_file || !attr->dentries.space_file
@@ -324,6 +418,7 @@ int init_fault_attr_dentries(struct faul
|| !attr->dentries.require_end_file
|| !attr->dentries.reject_start_file
|| !attr->dentries.reject_end_file
+ || !attr->dentries.uniquestack_depth_file
)
goto fail;

Index: linux-2.6.18/Documentation/fault-injection/fault-injection.txt
===================================================================
--- linux-2.6.18.orig/Documentation/fault-injection/fault-injection.txt
+++ linux-2.6.18/Documentation/fault-injection/fault-injection.txt
@@ -91,6 +91,13 @@ configuration of fault-injection capabil
for a caller within [require-start,require-end) OR
[reject-start,reject-end).

+- /debug/fail*/uniquestack-depth:
+
+ specifies the stacktrace depth walked during calculation of a
+ hash of caller's EIPs. Hash is compared against a record of
+ those already seen since boot; if duplicate, no failure is injected.
+ '0' disables the test.
+
- /debug/fail_page_alloc/ignore-gfp-highmem:

Format: { 'Y' | 'N' }

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