[PATCH tip/locking/core v2 1/2] lockdep: Refactor IRQ trace events fields into struct

[PATCH tip/locking/core v2 1/2] lockdep: Refactor IRQ trace events fields into struct

[Marco Elver]

Refactor the IRQ trace events fields, used for printing information
about the IRQ trace events, into a separate struct 'irqtrace_events'.

This improves readability by separating the information only used in
reporting, as well as enables (simplified) storing/restoring of
irqtrace_events snapshots.

No functional change intended.

Signed-off-by: Marco Elver <elver@google.com>
---
v2:
* Introduce patch, as pre-requisite to "kcsan: Improve IRQ state trace
  reporting".
---
 include/linux/irqflags.h | 13 +++++++++
 include/linux/sched.h    | 11 ++------
 kernel/fork.c            | 16 ++++-------
 kernel/locking/lockdep.c | 58 +++++++++++++++++++++-------------------
 4 files changed, 50 insertions(+), 48 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 5811ee8a5cd8..bd5c55755447 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -33,6 +33,19 @@
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 
+/* Per-task IRQ trace events information. */
+struct irqtrace_events {
+	unsigned int	irq_events;
+	unsigned long	hardirq_enable_ip;
+	unsigned long	hardirq_disable_ip;
+	unsigned int	hardirq_enable_event;
+	unsigned int	hardirq_disable_event;
+	unsigned long	softirq_disable_ip;
+	unsigned long	softirq_enable_ip;
+	unsigned int	softirq_disable_event;
+	unsigned int	softirq_enable_event;
+};
+
 DECLARE_PER_CPU(int, hardirqs_enabled);
 DECLARE_PER_CPU(int, hardirq_context);
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8d1de021b315..52e0fdd6a555 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/plist.h>
 #include <linux/hrtimer.h>
+#include <linux/irqflags.h>
 #include <linux/seccomp.h>
 #include <linux/nodemask.h>
 #include <linux/rcupdate.h>
@@ -980,17 +981,9 @@ struct task_struct {
 #endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
-	unsigned int			irq_events;
+	struct irqtrace_events		irqtrace;
 	unsigned int			hardirq_threaded;
-	unsigned long			hardirq_enable_ip;
-	unsigned long			hardirq_disable_ip;
-	unsigned int			hardirq_enable_event;
-	unsigned int			hardirq_disable_event;
 	u64				hardirq_chain_key;
-	unsigned long			softirq_disable_ip;
-	unsigned long			softirq_enable_ip;
-	unsigned int			softirq_disable_event;
-	unsigned int			softirq_enable_event;
 	int				softirqs_enabled;
 	int				softirq_context;
 	int				irq_config;
diff --git a/kernel/fork.c b/kernel/fork.c
index 70d9d0a4de2a..56a640799680 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2035,17 +2035,11 @@ static __latent_entropy struct task_struct *copy_process(
 	seqcount_init(&p->mems_allowed_seq);
 #endif
 #ifdef CONFIG_TRACE_IRQFLAGS
-	p->irq_events = 0;
-	p->hardirq_enable_ip = 0;
-	p->hardirq_enable_event = 0;
-	p->hardirq_disable_ip = _THIS_IP_;
-	p->hardirq_disable_event = 0;
-	p->softirqs_enabled = 1;
-	p->softirq_enable_ip = _THIS_IP_;
-	p->softirq_enable_event = 0;
-	p->softirq_disable_ip = 0;
-	p->softirq_disable_event = 0;
-	p->softirq_context = 0;
+	memset(&p->irqtrace, 0, sizeof(p->irqtrace));
+	p->irqtrace.hardirq_disable_ip	= _THIS_IP_;
+	p->irqtrace.softirq_enable_ip	= _THIS_IP_;
+	p->softirqs_enabled		= 1;
+	p->softirq_context		= 0;
 #endif
 
 	p->pagefault_disabled = 0;
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c9ea05edce25..7b5800374c40 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3484,19 +3484,21 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
 
 void print_irqtrace_events(struct task_struct *curr)
 {
-	printk("irq event stamp: %u\n", curr->irq_events);
+	const struct irqtrace_events *trace = &curr->irqtrace;
+
+	printk("irq event stamp: %u\n", trace->irq_events);
 	printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
-		curr->hardirq_enable_event, (void *)curr->hardirq_enable_ip,
-		(void *)curr->hardirq_enable_ip);
+		trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip,
+		(void *)trace->hardirq_enable_ip);
 	printk("hardirqs last disabled at (%u): [<%px>] %pS\n",
-		curr->hardirq_disable_event, (void *)curr->hardirq_disable_ip,
-		(void *)curr->hardirq_disable_ip);
+		trace->hardirq_disable_event, (void *)trace->hardirq_disable_ip,
+		(void *)trace->hardirq_disable_ip);
 	printk("softirqs last  enabled at (%u): [<%px>] %pS\n",
-		curr->softirq_enable_event, (void *)curr->softirq_enable_ip,
-		(void *)curr->softirq_enable_ip);
+		trace->softirq_enable_event, (void *)trace->softirq_enable_ip,
+		(void *)trace->softirq_enable_ip);
 	printk("softirqs last disabled at (%u): [<%px>] %pS\n",
-		curr->softirq_disable_event, (void *)curr->softirq_disable_ip,
-		(void *)curr->softirq_disable_ip);
+		trace->softirq_disable_event, (void *)trace->softirq_disable_ip,
+		(void *)trace->softirq_disable_ip);
 }
 
 static int HARDIRQ_verbose(struct lock_class *class)
@@ -3699,7 +3701,7 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_on_prepare);
 
 void noinstr lockdep_hardirqs_on(unsigned long ip)
 {
-	struct task_struct *curr = current;
+	struct irqtrace_events *trace = &current->irqtrace;
 
 	if (unlikely(!debug_locks))
 		return;
@@ -3752,8 +3754,8 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
 skip_checks:
 	/* we'll do an OFF -> ON transition: */
 	this_cpu_write(hardirqs_enabled, 1);
-	curr->hardirq_enable_ip = ip;
-	curr->hardirq_enable_event = ++curr->irq_events;
+	trace->hardirq_enable_ip = ip;
+	trace->hardirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(hardirqs_on_events);
 }
 EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
@@ -3763,8 +3765,6 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
  */
 void noinstr lockdep_hardirqs_off(unsigned long ip)
 {
-	struct task_struct *curr = current;
-
 	if (unlikely(!debug_locks))
 		return;
 
@@ -3784,12 +3784,14 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
 		return;
 
 	if (lockdep_hardirqs_enabled()) {
+		struct irqtrace_events *trace = &current->irqtrace;
+
 		/*
 		 * We have done an ON -> OFF transition:
 		 */
 		this_cpu_write(hardirqs_enabled, 0);
-		curr->hardirq_disable_ip = ip;
-		curr->hardirq_disable_event = ++curr->irq_events;
+		trace->hardirq_disable_ip = ip;
+		trace->hardirq_disable_event = ++trace->irq_events;
 		debug_atomic_inc(hardirqs_off_events);
 	} else {
 		debug_atomic_inc(redundant_hardirqs_off);
@@ -3802,7 +3804,7 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_off);
  */
 void lockdep_softirqs_on(unsigned long ip)
 {
-	struct task_struct *curr = current;
+	struct irqtrace_events *trace = &current->irqtrace;
 
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
@@ -3814,7 +3816,7 @@ void lockdep_softirqs_on(unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return;
 
-	if (curr->softirqs_enabled) {
+	if (current->softirqs_enabled) {
 		debug_atomic_inc(redundant_softirqs_on);
 		return;
 	}
@@ -3823,9 +3825,9 @@ void lockdep_softirqs_on(unsigned long ip)
 	/*
 	 * We'll do an OFF -> ON transition:
 	 */
-	curr->softirqs_enabled = 1;
-	curr->softirq_enable_ip = ip;
-	curr->softirq_enable_event = ++curr->irq_events;
+	current->softirqs_enabled = 1;
+	trace->softirq_enable_ip = ip;
+	trace->softirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(softirqs_on_events);
 	/*
 	 * We are going to turn softirqs on, so set the
@@ -3833,7 +3835,7 @@ void lockdep_softirqs_on(unsigned long ip)
 	 * enabled too:
 	 */
 	if (lockdep_hardirqs_enabled())
-		mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ);
+		mark_held_locks(current, LOCK_ENABLED_SOFTIRQ);
 	lockdep_recursion_finish();
 }
 
@@ -3842,8 +3844,6 @@ void lockdep_softirqs_on(unsigned long ip)
  */
 void lockdep_softirqs_off(unsigned long ip)
 {
-	struct task_struct *curr = current;
-
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
 
@@ -3853,13 +3853,15 @@ void lockdep_softirqs_off(unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return;
 
-	if (curr->softirqs_enabled) {
+	if (current->softirqs_enabled) {
+		struct irqtrace_events *trace = &current->irqtrace;
+
 		/*
 		 * We have done an ON -> OFF transition:
 		 */
-		curr->softirqs_enabled = 0;
-		curr->softirq_disable_ip = ip;
-		curr->softirq_disable_event = ++curr->irq_events;
+		current->softirqs_enabled = 0;
+		trace->softirq_disable_ip = ip;
+		trace->softirq_disable_event = ++trace->irq_events;
 		debug_atomic_inc(softirqs_off_events);
 		/*
 		 * Whoops, we wanted softirqs off, so why aren't they?
-- 
2.28.0.rc0.142.g3c755180ce-goog

[PATCH tip/locking/core v2 2/2] kcsan: Improve IRQ state trace reporting

[Marco Elver]

To improve the general usefulness of the IRQ state trace events with
KCSAN enabled, save and restore the trace information when entering and
exiting the KCSAN runtime as well as when generating a KCSAN report.

Without this, reporting the IRQ trace events (whether via a KCSAN report
or outside of KCSAN via a lockdep report) is rather useless due to
continuously being touched by KCSAN. This is because if KCSAN is
enabled, every instrumented memory access causes changes to IRQ trace
events (either by KCSAN disabling/enabling interrupts or taking
report_lock when generating a report).

Before "lockdep: Prepare for NMI IRQ state tracking", KCSAN avoided
touching the IRQ trace events via raw_local_irq_save/restore() and
lockdep_off/on().

Fixes: 248591f5d257 ("kcsan: Make KCSAN compatible with new IRQ state tracking")
Signed-off-by: Marco Elver <elver@google.com>
---
v2:
* Use simple struct copy, now that the IRQ trace events are in a struct.

Depends on:  "lockdep: Prepare for NMI IRQ state tracking"
---
 include/linux/sched.h |  4 ++++
 kernel/kcsan/core.c   | 23 +++++++++++++++++++++++
 kernel/kcsan/kcsan.h  |  7 +++++++
 kernel/kcsan/report.c |  3 +++
 4 files changed, 37 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 52e0fdd6a555..060e9214c8b5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1184,8 +1184,12 @@ struct task_struct {
 #ifdef CONFIG_KASAN
 	unsigned int			kasan_depth;
 #endif
+
 #ifdef CONFIG_KCSAN
 	struct kcsan_ctx		kcsan_ctx;
+#ifdef CONFIG_TRACE_IRQFLAGS
+	struct irqtrace_events		kcsan_save_irqtrace;
+#endif
 #endif
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 732623c30359..0fe068192781 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -291,6 +291,20 @@ static inline unsigned int get_delay(void)
 				0);
 }
 
+void kcsan_save_irqtrace(struct task_struct *task)
+{
+#ifdef CONFIG_TRACE_IRQFLAGS
+	task->kcsan_save_irqtrace = task->irqtrace;
+#endif
+}
+
+void kcsan_restore_irqtrace(struct task_struct *task)
+{
+#ifdef CONFIG_TRACE_IRQFLAGS
+	task->irqtrace = task->kcsan_save_irqtrace;
+#endif
+}
+
 /*
  * Pull everything together: check_access() below contains the performance
  * critical operations; the fast-path (including check_access) functions should
@@ -336,9 +350,11 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 	flags = user_access_save();
 
 	if (consumed) {
+		kcsan_save_irqtrace(current);
 		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
 			     KCSAN_REPORT_CONSUMED_WATCHPOINT,
 			     watchpoint - watchpoints);
+		kcsan_restore_irqtrace(current);
 	} else {
 		/*
 		 * The other thread may not print any diagnostics, as it has
@@ -396,6 +412,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 		goto out;
 	}
 
+	/*
+	 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
+	 * runtime is entered for every memory access, and potentially useful
+	 * information is lost if dirtied by KCSAN.
+	 */
+	kcsan_save_irqtrace(current);
 	if (!kcsan_interrupt_watcher)
 		local_irq_save(irq_flags);
 
@@ -539,6 +561,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 out_unlock:
 	if (!kcsan_interrupt_watcher)
 		local_irq_restore(irq_flags);
+	kcsan_restore_irqtrace(current);
 out:
 	user_access_restore(ua_flags);
 }
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 763d6d08d94b..29480010dc30 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -9,6 +9,7 @@
 #define _KERNEL_KCSAN_KCSAN_H
 
 #include <linux/kcsan.h>
+#include <linux/sched.h>
 
 /* The number of adjacent watchpoints to check. */
 #define KCSAN_CHECK_ADJACENT 1
@@ -22,6 +23,12 @@ extern unsigned int kcsan_udelay_interrupt;
  */
 extern bool kcsan_enabled;
 
+/*
+ * Save/restore IRQ flags state trace dirtied by KCSAN.
+ */
+void kcsan_save_irqtrace(struct task_struct *task);
+void kcsan_restore_irqtrace(struct task_struct *task);
+
 /*
  * Initialize debugfs file.
  */
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 6b2fb1a6d8cd..9d07e175de0f 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -308,6 +308,9 @@ static void print_verbose_info(struct task_struct *task)
 	if (!task)
 		return;
 
+	/* Restore IRQ state trace for printing. */
+	kcsan_restore_irqtrace(task);
+
 	pr_err("\n");
 	debug_show_held_locks(task);
 	print_irqtrace_events(task);
-- 
2.28.0.rc0.142.g3c755180ce-goog

[tip: locking/core] lockdep: Refactor IRQ trace events fields into struct

[tip-bot2 for Marco Elver]

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

Commit-ID:     9cd8b723f823d007bd70a3252e681fde07143f6d
Gitweb:        https://git.kernel.org/tip/9cd8b723f823d007bd70a3252e681fde07143f6d
Author:        Marco Elver <elver@google.com>
AuthorDate:    Wed, 29 Jul 2020 13:09:15 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 29 Jul 2020 16:30:40 +02:00

lockdep: Refactor IRQ trace events fields into struct

Refactor the IRQ trace events fields, used for printing information
about the IRQ trace events, into a separate struct 'irqtrace_events'.

This improves readability by separating the information only used in
reporting, as well as enables (simplified) storing/restoring of
irqtrace_events snapshots.

No functional change intended.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-1-elver@google.com
---
 include/linux/irqflags.h | 13 +++++++++-
 include/linux/sched.h    | 11 +------
 kernel/fork.c            | 16 +++--------
 kernel/locking/lockdep.c | 58 ++++++++++++++++++++-------------------
 4 files changed, 50 insertions(+), 48 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 5811ee8..bd5c557 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -33,6 +33,19 @@
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 
+/* Per-task IRQ trace events information. */
+struct irqtrace_events {
+	unsigned int	irq_events;
+	unsigned long	hardirq_enable_ip;
+	unsigned long	hardirq_disable_ip;
+	unsigned int	hardirq_enable_event;
+	unsigned int	hardirq_disable_event;
+	unsigned long	softirq_disable_ip;
+	unsigned long	softirq_enable_ip;
+	unsigned int	softirq_disable_event;
+	unsigned int	softirq_enable_event;
+};
+
 DECLARE_PER_CPU(int, hardirqs_enabled);
 DECLARE_PER_CPU(int, hardirq_context);
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9a9d826..26adabe 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/plist.h>
 #include <linux/hrtimer.h>
+#include <linux/irqflags.h>
 #include <linux/seccomp.h>
 #include <linux/nodemask.h>
 #include <linux/rcupdate.h>
@@ -980,17 +981,9 @@ struct task_struct {
 #endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
-	unsigned int			irq_events;
+	struct irqtrace_events		irqtrace;
 	unsigned int			hardirq_threaded;
-	unsigned long			hardirq_enable_ip;
-	unsigned long			hardirq_disable_ip;
-	unsigned int			hardirq_enable_event;
-	unsigned int			hardirq_disable_event;
 	u64				hardirq_chain_key;
-	unsigned long			softirq_disable_ip;
-	unsigned long			softirq_enable_ip;
-	unsigned int			softirq_disable_event;
-	unsigned int			softirq_enable_event;
 	int				softirqs_enabled;
 	int				softirq_context;
 	int				irq_config;
diff --git a/kernel/fork.c b/kernel/fork.c
index fc72f09..f831b82 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2035,17 +2035,11 @@ static __latent_entropy struct task_struct *copy_process(
 	seqcount_spinlock_init(&p->mems_allowed_seq, &p->alloc_lock);
 #endif
 #ifdef CONFIG_TRACE_IRQFLAGS
-	p->irq_events = 0;
-	p->hardirq_enable_ip = 0;
-	p->hardirq_enable_event = 0;
-	p->hardirq_disable_ip = _THIS_IP_;
-	p->hardirq_disable_event = 0;
-	p->softirqs_enabled = 1;
-	p->softirq_enable_ip = _THIS_IP_;
-	p->softirq_enable_event = 0;
-	p->softirq_disable_ip = 0;
-	p->softirq_disable_event = 0;
-	p->softirq_context = 0;
+	memset(&p->irqtrace, 0, sizeof(p->irqtrace));
+	p->irqtrace.hardirq_disable_ip	= _THIS_IP_;
+	p->irqtrace.softirq_enable_ip	= _THIS_IP_;
+	p->softirqs_enabled		= 1;
+	p->softirq_context		= 0;
 #endif
 
 	p->pagefault_disabled = 0;
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c9ea05e..7b58003 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3484,19 +3484,21 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
 
 void print_irqtrace_events(struct task_struct *curr)
 {
-	printk("irq event stamp: %u\n", curr->irq_events);
+	const struct irqtrace_events *trace = &curr->irqtrace;
+
+	printk("irq event stamp: %u\n", trace->irq_events);
 	printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
-		curr->hardirq_enable_event, (void *)curr->hardirq_enable_ip,
-		(void *)curr->hardirq_enable_ip);
+		trace->hardirq_enable_event, (void *)trace->hardirq_enable_ip,
+		(void *)trace->hardirq_enable_ip);
 	printk("hardirqs last disabled at (%u): [<%px>] %pS\n",
-		curr->hardirq_disable_event, (void *)curr->hardirq_disable_ip,
-		(void *)curr->hardirq_disable_ip);
+		trace->hardirq_disable_event, (void *)trace->hardirq_disable_ip,
+		(void *)trace->hardirq_disable_ip);
 	printk("softirqs last  enabled at (%u): [<%px>] %pS\n",
-		curr->softirq_enable_event, (void *)curr->softirq_enable_ip,
-		(void *)curr->softirq_enable_ip);
+		trace->softirq_enable_event, (void *)trace->softirq_enable_ip,
+		(void *)trace->softirq_enable_ip);
 	printk("softirqs last disabled at (%u): [<%px>] %pS\n",
-		curr->softirq_disable_event, (void *)curr->softirq_disable_ip,
-		(void *)curr->softirq_disable_ip);
+		trace->softirq_disable_event, (void *)trace->softirq_disable_ip,
+		(void *)trace->softirq_disable_ip);
 }
 
 static int HARDIRQ_verbose(struct lock_class *class)
@@ -3699,7 +3701,7 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_on_prepare);
 
 void noinstr lockdep_hardirqs_on(unsigned long ip)
 {
-	struct task_struct *curr = current;
+	struct irqtrace_events *trace = &current->irqtrace;
 
 	if (unlikely(!debug_locks))
 		return;
@@ -3752,8 +3754,8 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
 skip_checks:
 	/* we'll do an OFF -> ON transition: */
 	this_cpu_write(hardirqs_enabled, 1);
-	curr->hardirq_enable_ip = ip;
-	curr->hardirq_enable_event = ++curr->irq_events;
+	trace->hardirq_enable_ip = ip;
+	trace->hardirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(hardirqs_on_events);
 }
 EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
@@ -3763,8 +3765,6 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_on);
  */
 void noinstr lockdep_hardirqs_off(unsigned long ip)
 {
-	struct task_struct *curr = current;
-
 	if (unlikely(!debug_locks))
 		return;
 
@@ -3784,12 +3784,14 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
 		return;
 
 	if (lockdep_hardirqs_enabled()) {
+		struct irqtrace_events *trace = &current->irqtrace;
+
 		/*
 		 * We have done an ON -> OFF transition:
 		 */
 		this_cpu_write(hardirqs_enabled, 0);
-		curr->hardirq_disable_ip = ip;
-		curr->hardirq_disable_event = ++curr->irq_events;
+		trace->hardirq_disable_ip = ip;
+		trace->hardirq_disable_event = ++trace->irq_events;
 		debug_atomic_inc(hardirqs_off_events);
 	} else {
 		debug_atomic_inc(redundant_hardirqs_off);
@@ -3802,7 +3804,7 @@ EXPORT_SYMBOL_GPL(lockdep_hardirqs_off);
  */
 void lockdep_softirqs_on(unsigned long ip)
 {
-	struct task_struct *curr = current;
+	struct irqtrace_events *trace = &current->irqtrace;
 
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
@@ -3814,7 +3816,7 @@ void lockdep_softirqs_on(unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return;
 
-	if (curr->softirqs_enabled) {
+	if (current->softirqs_enabled) {
 		debug_atomic_inc(redundant_softirqs_on);
 		return;
 	}
@@ -3823,9 +3825,9 @@ void lockdep_softirqs_on(unsigned long ip)
 	/*
 	 * We'll do an OFF -> ON transition:
 	 */
-	curr->softirqs_enabled = 1;
-	curr->softirq_enable_ip = ip;
-	curr->softirq_enable_event = ++curr->irq_events;
+	current->softirqs_enabled = 1;
+	trace->softirq_enable_ip = ip;
+	trace->softirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(softirqs_on_events);
 	/*
 	 * We are going to turn softirqs on, so set the
@@ -3833,7 +3835,7 @@ void lockdep_softirqs_on(unsigned long ip)
 	 * enabled too:
 	 */
 	if (lockdep_hardirqs_enabled())
-		mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ);
+		mark_held_locks(current, LOCK_ENABLED_SOFTIRQ);
 	lockdep_recursion_finish();
 }
 
@@ -3842,8 +3844,6 @@ void lockdep_softirqs_on(unsigned long ip)
  */
 void lockdep_softirqs_off(unsigned long ip)
 {
-	struct task_struct *curr = current;
-
 	if (unlikely(!debug_locks || current->lockdep_recursion))
 		return;
 
@@ -3853,13 +3853,15 @@ void lockdep_softirqs_off(unsigned long ip)
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return;
 
-	if (curr->softirqs_enabled) {
+	if (current->softirqs_enabled) {
+		struct irqtrace_events *trace = &current->irqtrace;
+
 		/*
 		 * We have done an ON -> OFF transition:
 		 */
-		curr->softirqs_enabled = 0;
-		curr->softirq_disable_ip = ip;
-		curr->softirq_disable_event = ++curr->irq_events;
+		current->softirqs_enabled = 0;
+		trace->softirq_disable_ip = ip;
+		trace->softirq_disable_event = ++trace->irq_events;
 		debug_atomic_inc(softirqs_off_events);
 		/*
 		 * Whoops, we wanted softirqs off, so why aren't they?

[tip: locking/core] kcsan: Improve IRQ state trace reporting

[tip-bot2 for Marco Elver]

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

Commit-ID:     47490fdd411675707624fdfbf7bcfcd5f6a5e706
Gitweb:        https://git.kernel.org/tip/47490fdd411675707624fdfbf7bcfcd5f6a5e706
Author:        Marco Elver <elver@google.com>
AuthorDate:    Wed, 29 Jul 2020 13:09:16 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 29 Jul 2020 16:30:41 +02:00

kcsan: Improve IRQ state trace reporting

To improve the general usefulness of the IRQ state trace events with
KCSAN enabled, save and restore the trace information when entering and
exiting the KCSAN runtime as well as when generating a KCSAN report.

Without this, reporting the IRQ trace events (whether via a KCSAN report
or outside of KCSAN via a lockdep report) is rather useless due to
continuously being touched by KCSAN. This is because if KCSAN is
enabled, every instrumented memory access causes changes to IRQ trace
events (either by KCSAN disabling/enabling interrupts or taking
report_lock when generating a report).

Before "lockdep: Prepare for NMI IRQ state tracking", KCSAN avoided
touching the IRQ trace events via raw_local_irq_save/restore() and
lockdep_off/on().

Fixes: 248591f5d257 ("kcsan: Make KCSAN compatible with new IRQ state tracking")
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-2-elver@google.com
---
 include/linux/sched.h |  4 ++++
 kernel/kcsan/core.c   | 23 +++++++++++++++++++++++
 kernel/kcsan/kcsan.h  |  7 +++++++
 kernel/kcsan/report.c |  3 +++
 4 files changed, 37 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 26adabe..2ede13a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1184,8 +1184,12 @@ struct task_struct {
 #ifdef CONFIG_KASAN
 	unsigned int			kasan_depth;
 #endif
+
 #ifdef CONFIG_KCSAN
 	struct kcsan_ctx		kcsan_ctx;
+#ifdef CONFIG_TRACE_IRQFLAGS
+	struct irqtrace_events		kcsan_save_irqtrace;
+#endif
 #endif
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 732623c..0fe0681 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -291,6 +291,20 @@ static inline unsigned int get_delay(void)
 				0);
 }
 
+void kcsan_save_irqtrace(struct task_struct *task)
+{
+#ifdef CONFIG_TRACE_IRQFLAGS
+	task->kcsan_save_irqtrace = task->irqtrace;
+#endif
+}
+
+void kcsan_restore_irqtrace(struct task_struct *task)
+{
+#ifdef CONFIG_TRACE_IRQFLAGS
+	task->irqtrace = task->kcsan_save_irqtrace;
+#endif
+}
+
 /*
  * Pull everything together: check_access() below contains the performance
  * critical operations; the fast-path (including check_access) functions should
@@ -336,9 +350,11 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 	flags = user_access_save();
 
 	if (consumed) {
+		kcsan_save_irqtrace(current);
 		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
 			     KCSAN_REPORT_CONSUMED_WATCHPOINT,
 			     watchpoint - watchpoints);
+		kcsan_restore_irqtrace(current);
 	} else {
 		/*
 		 * The other thread may not print any diagnostics, as it has
@@ -396,6 +412,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 		goto out;
 	}
 
+	/*
+	 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
+	 * runtime is entered for every memory access, and potentially useful
+	 * information is lost if dirtied by KCSAN.
+	 */
+	kcsan_save_irqtrace(current);
 	if (!kcsan_interrupt_watcher)
 		local_irq_save(irq_flags);
 
@@ -539,6 +561,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 out_unlock:
 	if (!kcsan_interrupt_watcher)
 		local_irq_restore(irq_flags);
+	kcsan_restore_irqtrace(current);
 out:
 	user_access_restore(ua_flags);
 }
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 763d6d0..2948001 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -9,6 +9,7 @@
 #define _KERNEL_KCSAN_KCSAN_H
 
 #include <linux/kcsan.h>
+#include <linux/sched.h>
 
 /* The number of adjacent watchpoints to check. */
 #define KCSAN_CHECK_ADJACENT 1
@@ -23,6 +24,12 @@ extern unsigned int kcsan_udelay_interrupt;
 extern bool kcsan_enabled;
 
 /*
+ * Save/restore IRQ flags state trace dirtied by KCSAN.
+ */
+void kcsan_save_irqtrace(struct task_struct *task);
+void kcsan_restore_irqtrace(struct task_struct *task);
+
+/*
  * Initialize debugfs file.
  */
 void kcsan_debugfs_init(void);
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 6b2fb1a..9d07e17 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -308,6 +308,9 @@ static void print_verbose_info(struct task_struct *task)
 	if (!task)
 		return;
 
+	/* Restore IRQ state trace for printing. */
+	kcsan_restore_irqtrace(task);
+
 	pr_err("\n");
 	debug_show_held_locks(task);
 	print_irqtrace_events(task);