linux-kernel - Re: [driver-core PATCH v5 4/9] driver core: Move async_synchronize

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Message-ID: <1541466289.196084.176.camel@acm.org>
Date:   Mon, 05 Nov 2018 17:04:49 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Cc:     linux-nvdimm@...ts.01.org, tj@...nel.org,
        akpm@...ux-foundation.org, linux-pm@...r.kernel.org,
        jiangshanlai@...il.com, rafael@...nel.org, len.brown@...el.com,
        pavel@....cz, zwisler@...nel.org, dan.j.williams@...el.com,
        dave.jiang@...el.com
Subject: Re: [driver-core PATCH v5 4/9] driver core: Move
 async_synchronize_full call

On Mon, 2018-11-05 at 13:11 -0800, Alexander Duyck wrote:
> This patch moves the async_synchronize_full call out of
> __device_release_driver and into driver_detach.
> 
> The idea behind this is that the async_synchronize_full call will only
> guarantee that any existing async operations are flushed. This doesn't do
> anything to guarantee that a hotplug event that may occur while we are
> doing the release of the driver will not be asynchronously scheduled.
> 
> By moving this into the driver_detach path we can avoid potential deadlocks
> as we aren't holding the device lock at this point and we should not have
> the driver we want to flush loaded so the flush will take care of any
> asynchronous events the driver we are detaching might have scheduled.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> ---
>  drivers/base/dd.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 76c40fe69463..e74cefeb5b69 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -975,9 +975,6 @@ static void __device_release_driver(struct device *dev, struct device *parent)
>  
>  	drv = dev->driver;
>  	if (drv) {
> -		if (driver_allows_async_probing(drv))
> -			async_synchronize_full();
> -
>  		while (device_links_busy(dev)) {
>  			__device_driver_unlock(dev, parent);
>  
> @@ -1087,6 +1084,9 @@ void driver_detach(struct device_driver *drv)
>  	struct device_private *dev_prv;
>  	struct device *dev;
>  
> +	if (driver_allows_async_probing(drv))
> +		async_synchronize_full();
> +
>  	for (;;) {
>  		spin_lock(&drv->p->klist_devices.k_lock);
>  		if (list_empty(&drv->p->klist_devices.k_list)) {

Have you considered to move that async_synchronize_full() call into
bus_remove_driver()? Verifying the correctness of this patch requires to
check whether the async_synchronize_full() comes after the
klist_remove(&drv->p->knode_bus) call. That verification is easier when
the async_synchronize_full() call occurs in bus_remove_driver() instead
of in driver_detach().

Thanks,

Bart.