Re: [PATCH 04/11] cxl/core: Clamp max lock_class

[Dan Williams]

On Wed, Mar 9, 2022 at 10:27 AM Jonathan Cameron
 wrote:
>
> On Mon, 28 Feb 2022 18:49:11 -0800
> Dan Williams  wrote:
>
> > MAX_LOCKDEP_SUBCLASSES limits the depth of the CXL topology that can be
> > validated by lockdep. Given that the cxl_test topology is already at
> > this limit collapse some of the levels and clamp the max depth.
> >
> > Cc: Alison Schofield 
> > Cc: Vishal Verma 
> > Cc: Ira Weiny 
> > Cc: Ben Widawsky 
> > Signed-off-by: Dan Williams 
> > ---
> >  drivers/cxl/cxl.h |   21 +
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > index 97e6ca7e4940..1357a245037d 100644
> > --- a/drivers/cxl/cxl.h
> > +++ b/drivers/cxl/cxl.h
> > @@ -501,20 +501,33 @@ enum cxl_lock_class {
> >   CXL_ANON_LOCK,
> >   CXL_NVDIMM_LOCK,
> >   CXL_NVDIMM_BRIDGE_LOCK,
>
> I'd be tempted to give explicit value to the one above as well
> so it's immediate clear there is deliberate duplication here.

Sounds good.

I also notice that clamp_lock_class() should return -1 when it wants
to disable validation, not zero.

[PATCH 04/11] cxl/core: Clamp max lock_class

[Dan Williams]

MAX_LOCKDEP_SUBCLASSES limits the depth of the CXL topology that can be
validated by lockdep. Given that the cxl_test topology is already at
this limit collapse some of the levels and clamp the max depth.

Cc: Alison Schofield 
Cc: Vishal Verma 
Cc: Ira Weiny 
Cc: Ben Widawsky 
Signed-off-by: Dan Williams 
---
 drivers/cxl/cxl.h |   21 +
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 97e6ca7e4940..1357a245037d 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -501,20 +501,33 @@ enum cxl_lock_class {
CXL_ANON_LOCK,
CXL_NVDIMM_LOCK,
CXL_NVDIMM_BRIDGE_LOCK,
-   CXL_PORT_LOCK,
+   CXL_PORT_LOCK = 2,
/*
 * Be careful to add new lock classes here, CXL_PORT_LOCK is
 * extended by the port depth, so a maximum CXL port topology
-* depth would need to be defined first.
+* depth would need to be defined first. Also, the max
+* validation depth is limited by MAX_LOCKDEP_SUBCLASSES.
 */
 };
 
+static inline int clamp_lock_class(struct device *dev, int lock_class)
+{
+   if (lock_class >= MAX_LOCKDEP_SUBCLASSES) {
+   dev_warn_once(dev,
+ "depth: %d, disabling lockdep for this device\n",
+ lock_class);
+   return 0;
+   }
+
+   return lock_class;
+}
+
 static inline int cxl_lock_class(struct device *dev)
 {
if (is_cxl_port(dev)) {
struct cxl_port *port = to_cxl_port(dev);
 
-   return CXL_PORT_LOCK + port->depth;
+   return clamp_lock_class(dev, CXL_PORT_LOCK + port->depth);
} else if (is_cxl_decoder(dev)) {
struct cxl_port *port = to_cxl_port(dev->parent);
 
@@ -522,7 +535,7 @@ static inline int cxl_lock_class(struct device *dev)
 * A decoder is the immediate child of a port, so set
 * its lock class equal to other child device siblings.
 */
-   return CXL_PORT_LOCK + port->depth + 1;
+   return clamp_lock_class(dev, CXL_PORT_LOCK + port->depth + 1);
} else if (is_cxl_nvdimm_bridge(dev))
return CXL_NVDIMM_BRIDGE_LOCK;
else if (is_cxl_nvdimm(dev))