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kcsan: Introduce ASSERT_EXCLUSIVE_*() macros

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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: Paul E. McKenney <paulmck@kernel.org>
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 16:46:25 +01:00 committed by Ingo Molnar
parent d591ec3db7
commit f97f713dc2
1 changed files with 40 additions and 0 deletions
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40
include/linux/kcsan-checks.h
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@ -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 */