[tip: locking/kcsan] kcsan: Introduce kcsan_value_change type

From: tip-bot2 for Marco Elver
Date: Tue Mar 24 2020 - 05:12:39 EST

Next message: Masahiro Yamada: "Re: [PATCH] Documentation/changes: Raise minimum supported binutils version to 2.23"
Previous message: tip-bot2 for Marco Elver: "[tip: locking/kcsan] kcsan, trace: Make KCSAN compatible with tracing"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

The following commit has been merged into the locking/kcsan branch of tip:

Commit-ID: b738f6169f1260b4ed5bd9f220b1c84d79f3ab8d
Gitweb: https://git.kernel.org/tip/b738f6169f1260b4ed5bd9f220b1c84d79f3ab8d
Author: Marco Elver <elver@xxxxxxxxxx>
AuthorDate: Tue, 11 Feb 2020 17:04:21 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sat, 21 Mar 2020 09:44:03 +01:00

kcsan: Introduce kcsan_value_change type

Introduces kcsan_value_change type, which explicitly points out if we
either observed a value-change (TRUE), or we could not observe one but
cannot rule out a value-change happened (MAYBE). The MAYBE state can
either be reported or not, depending on configuration preferences.

A follow-up patch introduces the FALSE state, which should never be
reported.

No functional change intended.

Acked-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/kcsan/core.c | 38 ++++++++++++++++++++++----------------
kernel/kcsan/kcsan.h | 19 ++++++++++++++++++-
kernel/kcsan/report.c | 26 ++++++++++++++------------
3 files changed, 54 insertions(+), 29 deletions(-)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 498b1eb..3f89801 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -341,7 +341,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
u32 _4;
u64 _8;
} expect_value;
- bool value_change = false;
+ enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
unsigned long ua_flags = user_access_save();
unsigned long irq_flags;

@@ -398,6 +398,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
* Read the current value, to later check and infer a race if the data
* was modified via a non-instrumented access, e.g. from a device.
*/
+ expect_value._8 = 0;
switch (size) {
case 1:
expect_value._1 = READ_ONCE(*(const u8 *)ptr);
@@ -436,24 +437,37 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
*/
switch (size) {
case 1:
- value_change = expect_value._1 != READ_ONCE(*(const u8 *)ptr);
+ expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
break;
case 2:
- value_change = expect_value._2 != READ_ONCE(*(const u16 *)ptr);
+ expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
break;
case 4:
- value_change = expect_value._4 != READ_ONCE(*(const u32 *)ptr);
+ expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
break;
case 8:
- value_change = expect_value._8 != READ_ONCE(*(const u64 *)ptr);
+ expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
break;
default:
break; /* ignore; we do not diff the values */
}

+ /* Were we able to observe a value-change? */
+ if (expect_value._8 != 0)
+ value_change = KCSAN_VALUE_CHANGE_TRUE;
+
/* Check if this access raced with another. */
if (!remove_watchpoint(watchpoint)) {
/*
+ * Depending on the access type, map a value_change of MAYBE to
+ * TRUE (require reporting).
+ */
+ if (value_change == KCSAN_VALUE_CHANGE_MAYBE && (size > 8 || is_assert)) {
+ /* Always assume a value-change. */
+ value_change = KCSAN_VALUE_CHANGE_TRUE;
+ }
+
+ /*
* No need to increment 'data_races' counter, as the racing
* thread already did.
*
@@ -461,20 +475,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
* therefore both this thread and the racing thread may
* increment this counter.
*/
- if (is_assert)
+ if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

- /*
- * - If we were not able to observe a value change due to size
- * constraints, always assume a value change.
- * - If the access type is an assertion, we also always assume a
- * value change to always report the race.
- */
- value_change = value_change || size > 8 || is_assert;
-
kcsan_report(ptr, size, type, value_change, smp_processor_id(),
KCSAN_REPORT_RACE_SIGNAL);
- } else if (value_change) {
+ } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
/* Inferring a race, since the value should not have changed. */

kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
@@ -482,7 +488,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
- kcsan_report(ptr, size, type, true,
+ kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
smp_processor_id(),
KCSAN_REPORT_RACE_UNKNOWN_ORIGIN);
}
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 50078e7..83a79b0 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -88,6 +88,22 @@ extern void kcsan_counter_dec(enum kcsan_counter_id id);
*/
extern bool kcsan_skip_report_debugfs(unsigned long func_addr);

+/*
+ * Value-change states.
+ */
+enum kcsan_value_change {
+ /*
+ * Did not observe a value-change, however, it is valid to report the
+ * race, depending on preferences.
+ */
+ KCSAN_VALUE_CHANGE_MAYBE,
+
+ /*
+ * The value was observed to change, and the race should be reported.
+ */
+ KCSAN_VALUE_CHANGE_TRUE,
+};
+
enum kcsan_report_type {
/*
* The thread that set up the watchpoint and briefly stalled was
@@ -111,6 +127,7 @@ enum kcsan_report_type {
* Print a race report from thread that encountered the race.
*/
extern void kcsan_report(const volatile void *ptr, size_t size, int access_type,
- bool value_change, int cpu_id, enum kcsan_report_type type);
+ enum kcsan_value_change value_change, int cpu_id,
+ enum kcsan_report_type type);

#endif /* _KERNEL_KCSAN_KCSAN_H */
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index abf6852..d871476 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -130,26 +130,27 @@ static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
* Special rules to skip reporting.
*/
static bool
-skip_report(bool value_change, unsigned long top_frame)
+skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
{
/*
- * The first call to skip_report always has value_change==true, since we
+ * The first call to skip_report always has value_change==TRUE, since we
* cannot know the value written of an instrumented access. For the 2nd
* call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
*
- * 1. read watchpoint, conflicting write (value_change==true): report;
- * 2. read watchpoint, conflicting write (value_change==false): skip;
- * 3. write watchpoint, conflicting write (value_change==true): report;
- * 4. write watchpoint, conflicting write (value_change==false): skip;
- * 5. write watchpoint, conflicting read (value_change==false): skip;
- * 6. write watchpoint, conflicting read (value_change==true): report;
+ * 1. read watchpoint, conflicting write (value_change==TRUE): report;
+ * 2. read watchpoint, conflicting write (value_change==MAYBE): skip;
+ * 3. write watchpoint, conflicting write (value_change==TRUE): report;
+ * 4. write watchpoint, conflicting write (value_change==MAYBE): skip;
+ * 5. write watchpoint, conflicting read (value_change==MAYBE): skip;
+ * 6. write watchpoint, conflicting read (value_change==TRUE): report;
*
* Cases 1-4 are intuitive and expected; case 5 ensures we do not report
* data races where the write may have rewritten the same value; case 6
* is possible either if the size is larger than what we check value
* changes for or the access type is KCSAN_ACCESS_ASSERT.
*/
- if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && !value_change) {
+ if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) &&
+ value_change == KCSAN_VALUE_CHANGE_MAYBE) {
/*
* The access is a write, but the data value did not change.
*
@@ -245,7 +246,7 @@ static int sym_strcmp(void *addr1, void *addr2)
* Returns true if a report was generated, false otherwise.
*/
static bool print_report(const volatile void *ptr, size_t size, int access_type,
- bool value_change, int cpu_id,
+ enum kcsan_value_change value_change, int cpu_id,
enum kcsan_report_type type)
{
unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
@@ -258,7 +259,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
/*
* Must check report filter rules before starting to print.
*/
- if (skip_report(true, stack_entries[skipnr]))
+ if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
return false;

if (type == KCSAN_REPORT_RACE_SIGNAL) {
@@ -477,7 +478,8 @@ retry:
}

void kcsan_report(const volatile void *ptr, size_t size, int access_type,
- bool value_change, int cpu_id, enum kcsan_report_type type)
+ enum kcsan_value_change value_change, int cpu_id,
+ enum kcsan_report_type type)
{
unsigned long flags = 0;

Next message: Masahiro Yamada: "Re: [PATCH] Documentation/changes: Raise minimum supported binutils version to 2.23"
Previous message: tip-bot2 for Marco Elver: "[tip: locking/kcsan] kcsan, trace: Make KCSAN compatible with tracing"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]