linux-kernel - [PATCH 04/11] cxl/core: Clamp max lock

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Message-ID: <164610295187.2682974.18123746840987009597.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Mon, 28 Feb 2022 18:49:11 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     gregkh@...uxfoundation.org, rafael.j.wysocki@...el.com
Cc:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        nvdimm@...ts.linux.dev
Subject: [PATCH 04/11] cxl/core: Clamp max lock_class

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 <alison.schofield@...el.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Ben Widawsky <ben.widawsky@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 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))