[PATCH] nvme-tcp: Fix possible race of io_work and direct send

[Sagi Grimberg]

>> --- a/drivers/nvme/host/tcp.c
>> +++ b/drivers/nvme/host/tcp.c
> 
>> @@ -279,7 +289,7 @@ static inline void nvme_tcp_queue_request(struct nvme_tcp_request *req,
>>          if (queue->io_cpu == smp_processor_id() &&
>>              sync && empty && mutex_trylock(&queue->send_mutex)) {
> 
> but we can't rely on the processor id if we are on preemptible state..
> 
>    373.940336] BUG: using smp_processor_id() in preemptible [00000000]
> code: kworker/u8:4/457
> [  373.942037] caller is nvme_tcp_submit_async_event+0x4da/0x690 [nvme_tcp]
> [  373.942144] CPU: 0 PID: 457 Comm: kworker/u8:4 Not tainted 5.11.0-rc1+ #116
> [  373.942171] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
> [  373.942196] Workqueue: nvme-wq nvme_async_event_work [nvme_core]
> [  373.942259] Call Trace:
> [  373.942286]  dump_stack+0xd0/0x119
> [  373.942346]  check_preemption_disabled+0xec/0xf0
> [  373.942397]  nvme_tcp_submit_async_event+0x4da/0x690 [nvme_tcp]
> [  373.942449]  nvme_async_event_work+0x11d/0x1f0 [nvme_core]
> [  373.942496]  ? nvme_ctrl_loss_tmo_show+0x140/0x140 [nvme_core]
> [  373.942576]  process_one_work+0x9f3/0x1630
> [  373.942649]  ? pwq_dec_nr_in_flight+0x330/0x330
> [  373.942765]  worker_thread+0x9e/0xf60
> [  373.942849]  ? process_one_work+0x1630/0x1630
> [  373.942889]  kthread+0x362/0x480
> [  373.942918]  ? kthread_create_on_node+0x100/0x100

Well, this is a heuristic anyways, too bad we need to
disable preemption just for this...

I'm assuming that this makes the issue go away?
--
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index cf856103025a..ea07336ca179 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -281,8 +281,11 @@ static inline void nvme_tcp_queue_request(struct 
nvme_tcp_request *req,
                 bool sync, bool last)
  {
         struct nvme_tcp_queue *queue = req->queue;
+       int cpu;
         bool empty;

+       cpu = get_cpu();
+       put_cpu();
         empty = llist_add(&req->lentry, &queue->req_list) &&
                 list_empty(&queue->send_list) && !queue->request;

@@ -291,8 +294,8 @@ static inline void nvme_tcp_queue_request(struct 
nvme_tcp_request *req,
          * directly, otherwise queue io_work. Also, only do that if we
          * are on the same cpu, so we don't introduce contention.
          */
-       if (queue->io_cpu == smp_processor_id() &&
-           sync && empty && mutex_trylock(&queue->send_mutex)) {
+       if (queue->io_cpu == cpu && sync && empty &&
+           mutex_trylock(&queue->send_mutex)) {
                 queue->more_requests = !last;
                 nvme_tcp_send_all(queue);
                 queue->more_requests = false;

--