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kcsan: Add test to generate conflicts via debugfs

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Add 'test=<iters>' option to KCSAN's debugfs interface to invoke KCSAN
checks on a dummy variable. By writing 'test=<iters>' to the debugfs
file from multiple tasks, we can generate real conflicts, and trigger
data race reports.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Marco Elver 2020-02-06 16:46:26 +01:00 committed by Ingo Molnar
parent f97f713dc2
commit a312013578
1 changed files with 46 additions and 5 deletions
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51
kernel/kcsan/debugfs.c
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@ -6,6 +6,7 @@
#include <linux/debugfs.h> #include <linux/debugfs.h>
#include <linux/init.h> #include <linux/init.h>
#include <linux/kallsyms.h> #include <linux/kallsyms.h>
#include <linux/sched.h>
#include <linux/seq_file.h> #include <linux/seq_file.h>
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/sort.h> #include <linux/sort.h>
@ -69,9 +70,9 @@ void kcsan_counter_dec(enum kcsan_counter_id id)
/* /*
* The microbenchmark allows benchmarking KCSAN core runtime only. To run * The microbenchmark allows benchmarking KCSAN core runtime only. To run
* multiple threads, pipe 'microbench=<iters>' from multiple tasks into the * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
* debugfs file. * debugfs file. This will not generate any conflicts, and tests fast-path only.
*/ */
static void microbenchmark(unsigned long iters) static noinline void microbenchmark(unsigned long iters)
{ {
cycles_t cycles; cycles_t cycles;
@ -81,18 +82,52 @@ static void microbenchmark(unsigned long iters)
while (iters--) { while (iters--) {
/* /*
* We can run this benchmark from multiple tasks; this address * We can run this benchmark from multiple tasks; this address
* calculation increases likelyhood of some accesses overlapping * calculation increases likelyhood of some accesses
* (they still won't conflict because all are reads). * overlapping. Make the access type an atomic read, to never
* set up watchpoints and test the fast-path only.
*/ */
unsigned long addr = unsigned long addr =
iters % (CONFIG_KCSAN_NUM_WATCHPOINTS * PAGE_SIZE); iters % (CONFIG_KCSAN_NUM_WATCHPOINTS * PAGE_SIZE);
__kcsan_check_read((void *)addr, sizeof(long)); __kcsan_check_access((void *)addr, sizeof(long), KCSAN_ACCESS_ATOMIC);
} }
cycles = get_cycles() - cycles; cycles = get_cycles() - cycles;
pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles); pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
} }
/*
* Simple test to create conflicting accesses. Write 'test=<iters>' to KCSAN's
* debugfs file from multiple tasks to generate real conflicts and show reports.
*/
static long test_dummy;
static noinline void test_thread(unsigned long iters)
{
const struct kcsan_ctx ctx_save = current->kcsan_ctx;
cycles_t cycles;
/* We may have been called from an atomic region; reset context. */
memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
cycles = get_cycles();
while (iters--) {
__kcsan_check_read(&test_dummy, sizeof(test_dummy));
__kcsan_check_write(&test_dummy, sizeof(test_dummy));
ASSERT_EXCLUSIVE_WRITER(test_dummy);
ASSERT_EXCLUSIVE_ACCESS(test_dummy);
/* not actually instrumented */
WRITE_ONCE(test_dummy, iters); /* to observe value-change */
}
cycles = get_cycles() - cycles;
pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
/* restore context */
current->kcsan_ctx = ctx_save;
}
static int cmp_filterlist_addrs(const void *rhs, const void *lhs) static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
{ {
const unsigned long a = *(const unsigned long *)rhs; const unsigned long a = *(const unsigned long *)rhs;
@ -242,6 +277,12 @@ debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *o
if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters)) if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
return -EINVAL; return -EINVAL;
microbenchmark(iters); microbenchmark(iters);
} else if (!strncmp(arg, "test=", sizeof("test=") - 1)) {
unsigned long iters;
if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters))
return -EINVAL;
test_thread(iters);
} else if (!strcmp(arg, "whitelist")) { } else if (!strcmp(arg, "whitelist")) {
set_report_filterlist_whitelist(true); set_report_filterlist_whitelist(true);
} else if (!strcmp(arg, "blacklist")) { } else if (!strcmp(arg, "blacklist")) {