linux-kernel - Re: [driver-core PATCH v7 4/9] driver core: Probe devices asynchronously instead of the driver

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Message-ID: <20181201024847.GH28501@garbanzo.do-not-panic.com>
Date:   Fri, 30 Nov 2018 18:48:47 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.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,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        brendanhiggins@...gle.com
Subject: Re: [driver-core PATCH v7 4/9] driver core: Probe devices
 asynchronously instead of the driver

On Wed, Nov 28, 2018 at 04:32:26PM -0800, Alexander Duyck wrote:
> Probe devices asynchronously instead of the driver.

> +static void __driver_attach_async_helper(void *_dev, async_cookie_t cookie)
> +{
> +	struct device *dev = _dev;
> +	struct device_driver *drv;
> +
> +	__device_driver_lock(dev, dev->parent);
> +
> +	/*
> +	 * If someone attempted to bind a driver either successfully or
> +	 * unsuccessfully before we got here we should just skip the driver
> +	 * probe call.
> +	 */
> +	drv = dev_get_drv_async(dev);
> +	if (drv && !dev->driver)
> +		driver_probe_device(drv, dev);

I believe this should mean drivers which have async work on probe can
deadlock. For instance, if a driver does call async_schedule() or a
derivative call does this for it, the kernel will call
async_synchronize_full() and I believe we deadlock.

Are we sure most subsystems which would use async probe will not have
an async_schedule() call?

  Luis