linux-kernel - Re: [RFC] nvmet: Always remove processed AER elements from list

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Message-ID: <BYAPR04MB574907EE2666D6DA48DE30AD867C0@BYAPR04MB5749.namprd04.prod.outlook.com>
Date:   Sun, 3 Nov 2019 18:55:14 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     Christoph Hellwig <hch@....de>, Daniel Wagner <dwagner@...e.de>
CC:     Sagi Grimberg <sagi@...mberg.me>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: Re: [RFC] nvmet: Always remove processed AER elements from list

On 10/31/2019 07:51 AM, Christoph Hellwig wrote:
> On Wed, Oct 30, 2019 at 04:24:18PM +0100, Daniel Wagner wrote:
>> All async events are enqueued via nvmet_add_async_event() which
>> updates the ctrl->async_event_cmds[] array and additionally an struct
>> nvmet_async_event is added to the ctrl->async_events list.
>>
>> Under normal operations the nvmet_async_event_work() updates again the
>> ctrl->async_event_cmds and removes the corresponding struct
>> nvmet_async_event from the list again. Though nvmet_sq_destroy() could
>> be called which calles nvmet_async_events_free() which only updates
>> the ctrl->async_event_cmds[] array.
>>
>> Add a new function nvmet_async_events_process() which processes the
>> async events and updates both array and the list. With this we avoid
>> having two places where the array and list are modified.
>
> I don't think this patch is correct.  We can have AEN commands pending
> that aren't used - that is the host sent the command, but the target
> did not have even event yet.  That means the command sits in
> async_event_cmds, but there is no entry in >async_events for it yet.
>
> That being said I think what we want is to do the loop in your new
> nvmet_async_events_free first, but after that still call the loop in
> the existing nvmet_async_events_free after that.  That ensures we first
> flush out everything in ->async_events, and then also return any
> potential remaining entry.
>
Something like following on the top of this patch ?
(compile tested only).

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index b1b9dc58c3b4..36a859082846 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -153,6 +153,18 @@ static void nvmet_async_events_process(struct 
nvmet_ctrl *ctrl, u16 status)
                 mutex_unlock(&ctrl->lock);
                 nvmet_req_complete(req, status);
         }
+
+       while (1) {
+               mutex_lock(&ctrl->lock);
+               if (!ctrl->nr_async_event_cmds) {
+                       mutex_unlock(&ctrl->lock);
+                       return;
+               }
+
+               req = ctrl->async_event_cmds[--ctrl->nr_async_event_cmds];
+               mutex_unlock(&ctrl->lock);
+               nvmet_req_complete(req, NVME_SC_INTERNAL | NVME_SC_DNR);
+       }
  }

  static void nvmet_async_events_free(struct nvmet_ctrl *ctrl)