[PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Gregory Price]

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@gourry.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);
+		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

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Dave Jiang]

On 2/10/26 8:43 AM, 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@gourry.net>

Reivewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  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);
> +		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);
>  }
>  
>  /*

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Ira Weiny]

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@gourry.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
> 

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Gregory Price]

On Tue, Feb 10, 2026 at 01:44:06PM -0600, Ira Weiny wrote:
> Gregory Price wrote:
> > 
> > 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.
> 

lol i pointed out that this patch was a claude recommendation on the
initial report - didn't look to hard because it fixed this specific
deadlock with:

	if (cxlmd->attach && !cxlmd->dev.driver)
		break;

so yeah, easy enough to fixup.

I can either v2 or Dave if you want to just make the oneline change
before pull let me know

~Gregory

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[dan.j.williams]

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.

Whoops, yes, good catch, but...

> 
> Fixes: 29317f8dc6ed ("cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation")
> Signed-off-by: Gregory Price <gourry@gourry.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);

...please just make a helper cxl_memdev_did_attach(), and move the
existing comment there. No need for the addtional comment that just adds
narration.

> +	scoped_guard(device, &cxlmd->dev) {

In general, I feel that scoped_guard() is almost always the wrong choice
for existing code and a helper with plain guard() is preferred.

> +		if (cxlmd->attach && !cxlmd->dev.driver)
> +			break;
> +
> +		rc = devm_add_action_or_reset(cxlmd->cxlds->dev,
> +					      cxl_memdev_unregister, cxlmd);

Just for completeness, no need to hold the lock over this. The helper
can just check ->attach and ->dev.driver.

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Dave Jiang]

On 2/10/26 3:46 PM, Gregory Price wrote:
> On Tue, Feb 10, 2026 at 01:44:06PM -0600, Ira Weiny wrote:
>> Gregory Price wrote:
>>>
>>> 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.
>>
> 
> lol i pointed out that this patch was a claude recommendation on the
> initial report - didn't look to hard because it fixed this specific
> deadlock with:
> 
> 	if (cxlmd->attach && !cxlmd->dev.driver)
> 		break;
> 
> so yeah, easy enough to fixup.
> 
> I can either v2 or Dave if you want to just make the oneline change
> before pull let me know

With Dan's comments, may as we spin v2. We have time until rc1 releases.

> 
> ~Gregory

Re: [PATCH] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Gregory Price]

On Tue, Feb 10, 2026 at 04:20:35PM -0700, Dave Jiang wrote:
> 
> 
> > I can either v2 or Dave if you want to just make the oneline change
> > before pull let me know
> 
> With Dan's comments, may as we spin v2. We have time until rc1 releases.
> 

will get it first thing tomorrow

~Gregory