Commit f97f713d authored by Marco Elver's avatar Marco Elver Committed by Ingo Molnar
Browse files

kcsan: Introduce ASSERT_EXCLUSIVE_*() macros 



Introduces ASSERT_EXCLUSIVE_WRITER() and ASSERT_EXCLUSIVE_ACCESS(), which
may be used to assert properties of synchronization logic, where
violation cannot be detected as a normal data race.

Examples of the reports that may be generated:

    ==================================================================
    BUG: KCSAN: assert: race in test_thread / test_thread

    write to 0xffffffffab3d1540 of 8 bytes by task 466 on cpu 2:
     test_thread+0x8d/0x111
     debugfs_write.cold+0x32/0x44
     ...

    assert no writes to 0xffffffffab3d1540 of 8 bytes by task 464 on cpu 0:
     test_thread+0xa3/0x111
     debugfs_write.cold+0x32/0x44
     ...
    ==================================================================

    ==================================================================
    BUG: KCSAN: assert: race in test_thread / test_thread

    assert no accesses to 0xffffffffab3d1540 of 8 bytes by task 465 on cpu 1:
     test_thread+0xb9/0x111
     debugfs_write.cold+0x32/0x44
     ...

    read to 0xffffffffab3d1540 of 8 bytes by task 464 on cpu 0:
     test_thread+0x77/0x111
     debugfs_write.cold+0x32/0x44
     ...
    ==================================================================

Suggested-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d591ec3d

include/linux/kcsan-checks.h

+40 −0
Original line number Diff line number Diff line
@@ -96,4 +96,44 @@ static inline void kcsan_check_access(const volatile void *ptr, size_t size, 
	kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)

#endif



/**

 * ASSERT_EXCLUSIVE_WRITER - assert no other threads are writing @var

 *

 * Assert that there are no other threads writing @var; other readers are

 * allowed. This assertion can be used to specify properties of concurrent code,

 * where violation cannot be detected as a normal data race.

 *

 * For example, if a per-CPU variable is only meant to be written by a single

 * CPU, but may be read from other CPUs; in this case, reads and writes must be

 * marked properly, however, if an off-CPU WRITE_ONCE() races with the owning

 * CPU's WRITE_ONCE(), would not constitute a data race but could be a harmful

 * race condition. Using this macro allows specifying this property in the code

 * and catch such bugs.

 *

 * @var variable to assert on

 */

#define ASSERT_EXCLUSIVE_WRITER(var)                                           \

	__kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_ASSERT)



/**

 * ASSERT_EXCLUSIVE_ACCESS - assert no other threads are accessing @var

 *

 * Assert that no other thread is accessing @var (no readers nor writers). This

 * assertion can be used to specify properties of concurrent code, where

 * violation cannot be detected as a normal data race.

 *

 * For example, in a reference-counting algorithm where exclusive access is

 * expected after the refcount reaches 0. We can check that this property

 * actually holds as follows:

 *

 *	if (refcount_dec_and_test(&obj->refcnt)) {

 *		ASSERT_EXCLUSIVE_ACCESS(*obj);

 *		safely_dispose_of(obj);

 *	}

 *

 * @var variable to assert on

 */

#define ASSERT_EXCLUSIVE_ACCESS(var)                                           \

	__kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT)



#endif /* _LINUX_KCSAN_CHECKS_H */