Commit 2e986b81 authored by Marco Elver's avatar Marco Elver Committed by Paul E. McKenney
Browse files

kcsan: Optimize debugfs stats counters 



Remove kcsan_counter_inc/dec() functions, as they perform no other
logic, and are no longer needed.

This avoids several calls in kcsan_setup_watchpoint() and
kcsan_found_watchpoint(), as well as lets the compiler warn us about
potential out-of-bounds accesses as the array's size is known at all
usage sites at compile-time.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 178a1877

kernel/kcsan/core.c

+11 −11
Original line number Diff line number Diff line
@@ -367,13 +367,13 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr, 
		 * already removed the watchpoint, or another thread consumed

		 * the watchpoint before this thread.

		 */

		kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);

	}



	if ((type & KCSAN_ACCESS_ASSERT) != 0)

		kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

	else

		kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);



	user_access_restore(flags);

}
@@ -414,7 +414,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
		goto out;



	if (!check_encodable((unsigned long)ptr, size)) {

		kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);

		goto out;

	}
@@ -434,12 +434,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
		 * with which should_watch() returns true should be tweaked so

		 * that this case happens very rarely.

		 */

		kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);

		goto out_unlock;

	}



	kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS);

	kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS);

	atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);

	atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);



	/*

	 * Read the current value, to later check and infer a race if the data
@@ -541,16 +541,16 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
		 * increment this counter.

		 */

		if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)

			kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

			atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);



		kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,

			     watchpoint - watchpoints);

	} 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);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);

		if (is_assert)

			kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

			atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);



		if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)

			kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
@@ -563,7 +563,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
	 * reused after this point.

	 */

	remove_watchpoint(watchpoint);

	kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);

	atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);

out_unlock:

	if (!kcsan_interrupt_watcher)

		local_irq_restore(irq_flags);

kernel/kcsan/debugfs.c

+5 −16
Original line number Diff line number Diff line
@@ -17,10 +17,7 @@ 


#include "kcsan.h"



/*

 * Statistics counters.

 */

static atomic_long_t counters[KCSAN_COUNTER_COUNT];

atomic_long_t kcsan_counters[KCSAN_COUNTER_COUNT];

static const char *const counter_names[] = {

	[KCSAN_COUNTER_USED_WATCHPOINTS]		= "used_watchpoints",

	[KCSAN_COUNTER_SETUP_WATCHPOINTS]		= "setup_watchpoints",
@@ -53,16 +50,6 @@ static struct { 
};

static DEFINE_SPINLOCK(report_filterlist_lock);



void kcsan_counter_inc(enum kcsan_counter_id id)

{

	atomic_long_inc(&counters[id]);

}



void kcsan_counter_dec(enum kcsan_counter_id id)

{

	atomic_long_dec(&counters[id]);

}



/*

 * The microbenchmark allows benchmarking KCSAN core runtime only. To run

 * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
@@ -206,8 +193,10 @@ static int show_info(struct seq_file *file, void *v) 


	/* show stats */

	seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));

	for (i = 0; i < KCSAN_COUNTER_COUNT; ++i)

		seq_printf(file, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i]));

	for (i = 0; i < KCSAN_COUNTER_COUNT; ++i) {

		seq_printf(file, "%s: %ld\n", counter_names[i],

			   atomic_long_read(&kcsan_counters[i]));

	}



	/* show filter functions, and filter type */

	spin_lock_irqsave(&report_filterlist_lock, flags);

kernel/kcsan/kcsan.h

+6 −6
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#ifndef _KERNEL_KCSAN_KCSAN_H

#define _KERNEL_KCSAN_KCSAN_H



#include <linux/atomic.h>

#include <linux/kcsan.h>

#include <linux/sched.h>
@@ -34,6 +35,10 @@ void kcsan_restore_irqtrace(struct task_struct *task); 
 */

void kcsan_debugfs_init(void);



/*

 * Statistics counters displayed via debugfs; should only be modified in

 * slow-paths.

 */

enum kcsan_counter_id {

	/*

	 * Number of watchpoints currently in use.
@@ -86,12 +91,7 @@ enum kcsan_counter_id { 


	KCSAN_COUNTER_COUNT, /* number of counters */

};



/*

 * Increment/decrement counter with given id; avoid calling these in fast-path.

 */

extern void kcsan_counter_inc(enum kcsan_counter_id id);

extern void kcsan_counter_dec(enum kcsan_counter_id id);

extern atomic_long_t kcsan_counters[KCSAN_COUNTER_COUNT];



/*

 * Returns true if data races in the function symbol that maps to func_addr

kernel/kcsan/report.c

+1 −1
Original line number Diff line number Diff line
@@ -559,7 +559,7 @@ static bool prepare_report_consumer(unsigned long *flags, 
		 * If the actual accesses to not match, this was a false

		 * positive due to watchpoint encoding.

		 */

		kcsan_counter_inc(KCSAN_COUNTER_ENCODING_FALSE_POSITIVES);

		atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ENCODING_FALSE_POSITIVES]);

		goto discard;

	}

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