diff options
| author | Qian Cai <cai@lca.pw> | 2020-02-11 08:54:15 -0500 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-06-29 12:04:48 -0700 |
| commit | 33190b675ce2eacbeb4e75168c05b41110b506ec (patch) | |
| tree | c1290359ba769363b2d0bdbaebd169b86d716b85 /kernel/locking | |
| parent | 1fe84fd4a4027a17d511a832f89ab14107650ba4 (diff) | |
locking/osq_lock: Annotate a data race in osq_lock
The prev->next pointer can 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>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/osq_lock.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 1f7734949ac8..1de006ed3aa8 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; |