linux-kernel - Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev

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Message-ID: <698b8a8620f2a_dce1110074@iweiny-mobl.notmuch>
Date: Tue, 10 Feb 2026 13:44:06 -0600
From: Ira Weiny <ira.weiny@...el.com>
To: Gregory Price <gourry@...rry.net>, <linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <kernel-team@...a.com>,
	<dave@...olabs.net>, <jonathan.cameron@...wei.com>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
	<ira.weiny@...el.com>, <dan.j.williams@...el.com>
Subject: Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on
 attach failure

Gregory Price wrote:
> cxl_memdev_autoremove() takes device_lock(&cxlmd->dev) via guard(device)
> and then calls cxl_memdev_unregister() when the attach callback was
> provided but cxl_mem_probe() failed to bind.
> 
> cxl_memdev_unregister() calls
>   cdev_device_del()
>     device_del()
>       bus_remove_device()
>         device_release_driver()
> 
> which also takes device_lock(), deadlocking the calling thread.
> 
> This path is reached when a driver uses the @attach parameter to
> devm_cxl_add_memdev() and the CXL topology fails to enumerate (e.g.
> DVSEC range registers decode outside platform-defined CXL ranges,
> causing the endpoint port probe to fail).
> 
> Fix by using scoped_guard() and breaking out of the guard scope before
> calling cxl_memdev_unregister(), so device_lock() is released first.
> 
> Fixes: 29317f8dc6ed ("cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation")
> Signed-off-by: Gregory Price <gourry@...rry.net>
> ---
>  drivers/cxl/core/memdev.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index af3d0cc65138..c0de767b24fb 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -1098,19 +1098,22 @@ static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd)
>  	 * return. Note that failure here could be the result of a race to
>  	 * teardown the CXL port topology. I.e. cxl_mem_probe() could have
>  	 * succeeded and then cxl_mem unbound before the lock is acquired.
> +	 *
> +	 * Check under device_lock but unregister outside of it, as
> +	 * cxl_memdev_unregister() will also take the device lock.
>  	 */
> -	guard(device)(&cxlmd->dev);
> -	if (cxlmd->attach && !cxlmd->dev.driver) {
> -		cxl_memdev_unregister(cxlmd);
> -		return ERR_PTR(-ENXIO);
> +	scoped_guard(device, &cxlmd->dev) {
> +		if (cxlmd->attach && !cxlmd->dev.driver)
> +			break;
> +
> +		rc = devm_add_action_or_reset(cxlmd->cxlds->dev,
> +					      cxl_memdev_unregister, cxlmd);

This kind of threw me...  Won't this deadlock if
devm_add_action_or_reset() fails as well?

Need to use devm_add_action() and drop out of the guard on failure.

Ira

> +		if (rc)
> +			return ERR_PTR(rc);
> +		return cxlmd;
>  	}
> -
> -	rc = devm_add_action_or_reset(cxlmd->cxlds->dev, cxl_memdev_unregister,
> -				      cxlmd);
> -	if (rc)
> -		return ERR_PTR(rc);
> -
> -	return cxlmd;
> +	cxl_memdev_unregister(cxlmd);
> +	return ERR_PTR(-ENXIO);
>  }
>  
>  /*
> -- 
> 2.53.0
>