lkml.org 
[lkml]   [2021]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v5 2/6] nbd: make sure request completion won't concurrent
From
Date
On 2021/09/14 8:57, Ming Lei wrote:
> On Thu, Sep 09, 2021 at 10:12:52PM +0800, Yu Kuai wrote:
>> commit cddce0116058 ("nbd: Aovid double completion of a request")
>> try to fix that nbd_clear_que() and recv_work() can complete a
>> request concurrently. However, the problem still exists:
>>
>> t1 t2 t3
>>
>> nbd_disconnect_and_put
>> flush_workqueue
>> recv_work
>> blk_mq_complete_request
>> blk_mq_complete_request_remote -> this is true
>> WRITE_ONCE(rq->state, MQ_RQ_COMPLETE)
>> blk_mq_raise_softirq
>> blk_done_softirq
>> blk_complete_reqs
>> nbd_complete_rq
>> blk_mq_end_request
>> blk_mq_free_request
>> WRITE_ONCE(rq->state, MQ_RQ_IDLE)
>> nbd_clear_que
>> blk_mq_tagset_busy_iter
>> nbd_clear_req
>> __blk_mq_free_request
>> blk_mq_put_tag
>> blk_mq_complete_request -> complete again
>>
>> There are three places where request can be completed in nbd:
>> recv_work(), nbd_clear_que() and nbd_xmit_timeout(). Since they
>> all hold cmd->lock before completing the request, it's easy to
>> avoid the problem by setting and checking a cmd flag.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>> drivers/block/nbd.c | 11 +++++++++--
>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>> index 04861b585b62..550c8dc438ac 100644
>> --- a/drivers/block/nbd.c
>> +++ b/drivers/block/nbd.c
>> @@ -406,7 +406,11 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
>> if (!mutex_trylock(&cmd->lock))
>> return BLK_EH_RESET_TIMER;
>>
>> - __clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
>> + if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
>> + mutex_unlock(&cmd->lock);
>> + return BLK_EH_DONE;
>> + }
>> +
>> if (!refcount_inc_not_zero(&nbd->config_refs)) {
>> cmd->status = BLK_STS_TIMEOUT;
>> mutex_unlock(&cmd->lock);
>> @@ -842,7 +846,10 @@ static bool nbd_clear_req(struct request *req, void *data, bool reserved)
>>
>> mutex_lock(&cmd->lock);
>> cmd->status = BLK_STS_IOERR;
>> - __clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
>> + if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
>> + mutex_unlock(&cmd->lock);
>> + return true;
>> + }
>> mutex_unlock(&cmd->lock);
>
> If this request has completed from other code paths, ->status shouldn't be
> updated here, maybe it is done successfully.

Hi, Ming

Will change this in next iteration.

Thanks,
Kuai

\
 
 \ /
  Last update: 2021-09-14 05:12    [W:0.058 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site