The following commit has been merged into the locking/kcsan branch of tip: Commit-ID: f97f713dc25714ac13f3b5abdeffce2da3f6fe70 Gitweb: https://git.kernel.org/tip/f97f713dc25714ac13f3b5abdeffce2da3f6fe70 Author: Marco Elver <elver@xxxxxxxxxx> AuthorDate: Thu, 06 Feb 2020 16:46:25 +01:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Sat, 21 Mar 2020 09:42:59 +01:00 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: Paul E. McKenney <paulmck@xxxxxxxxxx> Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- include/linux/kcsan-checks.h | 40 +++++++++++++++++++++++++++++++++++- 1 file changed, 40 insertions(+) diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h index 5dcadc2..cf69617 100644 --- a/include/linux/kcsan-checks.h +++ b/include/linux/kcsan-checks.h @@ -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 */
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