linux-kernel - Re: [driver-core PATCH v7 1/9] driver core: Move async_synchronize

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Message-ID: <20181130232137.GE28501@garbanzo.do-not-panic.com>
Date:   Fri, 30 Nov 2018 15:21:37 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        dmitry.torokhov@...il.com
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        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, bvanassche@....org
Subject: Re: [driver-core PATCH v7 1/9] driver core: Move
 async_synchronize_full call

On Wed, Nov 28, 2018 at 04:32:11PM -0800, Alexander Duyck wrote:
> Move 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.
> 
> Fixes: 765230b5f084 ("driver-core: add asynchronous probing support for drivers")
> Reviewed-by: Bart Van Assche <bvanassche@....org>
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

  Luis

> ---
>  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 689ac9dc6d81..88713f182086 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -931,9 +931,6 @@ 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_unlock(dev);
>  			if (parent)
> @@ -1039,6 +1036,9 @@ 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)) {
>