Messages in this thread Patch in this message | | | From | Qian Cai <> | Subject | [PATCH -next v2] locking/osq_lock: annotate a data race in osq_lock | Date | Tue, 11 Feb 2020 08:54:15 -0500 |
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prev->next could be accessed concurrently as noticed by KCSAN,
write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107: osq_lock+0x25f/0x350 osq_wait_next at kernel/locking/osq_lock.c:79 (inlined by) osq_lock at kernel/locking/osq_lock.c:185 rwsem_optimistic_spin <snip>
read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100: osq_lock+0x196/0x350 osq_lock at kernel/locking/osq_lock.c:157 rwsem_optimistic_spin <snip>
Since the write only stores NULL to prev->next and the read tests if prev->next equals to this_cpu_ptr(&osq_node). Even if the value is shattered, the code is still working correctly. Thus, mark it as an intentional data race using the data_race() macro.
Signed-off-by: Qian Cai <cai@lca.pw> ---
v2: insert some code comments.
kernel/locking/osq_lock.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 1f7734949ac8..f733bcd99e8a 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -154,7 +154,11 @@ bool osq_lock(struct optimistic_spin_queue *lock) */ for (;;) { - if (prev->next == node && + /* + * cpu_relax() below implies a compiler barrier which would + * prevent this comparison being optimized away. + */ + if (data_race(prev->next == node) && cmpxchg(&prev->next, node, NULL) == node) break; -- 1.8.3.1
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