linux-kernel - Re: [PATCH] vmbus: remove hv_event_tasklet

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Message-ID: <20170317161505.0270a1b6@xeon-e3>
Date:   Fri, 17 Mar 2017 16:15:05 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Stephen Hemminger" <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vmbus: remove hv_event_tasklet_disable/enable

On Thu, 2 Mar 2017 12:32:55 +0000
Dexuan Cui <decui@...rosoft.com> wrote:

> With the recent introduction of per-channel tasklet, we need to update
> the way we handle the 3 concurrency issues:
> 
> 1. hv_process_channel_removal -> percpu_channel_deq vs.
>    vmbus_chan_sched -> list_for_each_entry(..., percpu_list);
> 
> 2. vmbus_process_offer -> percpu_channel_enq/deq vs. vmbus_chan_sched.
> 
> 3. vmbus_close_internal vs. the per-channel tasklet vmbus_on_event;
> 
> The first 2 issues can be handled by Stephen's recent patch
> "vmbus: use rcu for per-cpu channel list", and the third issue
> can be handled by calling tasklet_disable in vmbus_close_internal here.
> 
> We don't need the original hv_event_tasklet_disable/enable since we
> now use per-channel tasklet instead of the previous per-CPU tasklet,
> and actually we must remove them due to the side effect now:
> vmbus_process_offer -> hv_event_tasklet_enable -> tasklet_schedule will
> start the per-channel callback prematurely, cauing NULL dereferencing
> (the channel may haven't been properly configured to run the callback yet).
> 
> Fixes: 631e63a9f346 ("vmbus: change to per channel tasklet")
> 
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>

It also fixes a number of missed interrupts causing stuck tasks on boot.
Please put it in 4.11

Reviewed-by: Stephen Hemminger <sthemmin@...rosoft.com>