(+Luis)
On 2020-05-28 02:29, Jan Kara wrote:
> Mostly for historical reasons, q->blk_trace is assigned through xchg()
> and cmpxchg() atomic operations. Although this is correct, sparse
> complains about this because it violates rcu annotations. Furthermore
> there's no real need for atomic operations anymore since all changes to
> q->blk_trace happen under q->blk_trace_mutex. So let's just replace
> xchg() with rcu_replace_pointer() and cmpxchg() with explicit check and
> rcu_assign_pointer(). This makes the code more efficient and sparse
> happy.
>
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
How about adding a reference to commit c780e86dd48e ("blktrace: Protect
q->blk_trace with RCU") in the description of this patch?
> @@ -1669,10 +1672,7 @@ static int blk_trace_setup_queue(struct request_queue *q,
>
> blk_trace_setup_lba(bt, bdev);
>
> - ret = -EBUSY;
> - if (cmpxchg(&q->blk_trace, NULL, bt))
> - goto free_bt;
> -
> + rcu_assign_pointer(q->blk_trace, bt);
> get_probe_ref();
> return 0;
This changes a conditional assignment of q->blk_trace into an
unconditional assignment. Shouldn't q->blk_trace only be assigned if
q->blk_trace == NULL?
Thanks,
Bart.
