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

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Message-ID: <20191031145127.GC6024@lst.de>
Date:   Thu, 31 Oct 2019 15:51:27 +0100
From:   Christoph Hellwig <hch@....de>
To:     Daniel Wagner <dwagner@...e.de>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Johannes Thumshirn <jthumshirn@...e.de>
Subject: Re: [RFC] nvmet: Always remove processed AER elements from list

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.