linux-kernel - [PATCH v2 05/12] cxl/core: Clamp max lock

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Message-ID: <164982971542.684294.12980151056534955888.stgit@dwillia2-desk3.amr.corp.intel.com>
Date:   Tue, 12 Apr 2022 23:01:55 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-cxl@...r.kernel.org
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>,
        Dave Jiang <dave.jiang@...el.com>,
        Kevin Tian <kevin.tian@...el.com>, peterz@...radead.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev
Subject: [PATCH v2 05/12] 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>
Reviewed-by: Dave Jiang <dave.jiang@...el.com>
Reviewed-by: Kevin Tian <kevin.tian@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/cxl/cxl.h |   25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index a6c1a027e389..b86aac8cde4f 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -410,20 +410,37 @@ enum cxl_lock_class {
 	CXL_ANON_LOCK,
 	CXL_NVDIMM_LOCK,
 	CXL_NVDIMM_BRIDGE_LOCK,
-	CXL_PORT_LOCK,
+	/*
+	 * Collapse the compatible port and nvdimm-bridge lock classes
+	 * to save space
+	 */
+	CXL_PORT_LOCK = CXL_NVDIMM_BRIDGE_LOCK,
 	/*
 	 * 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 -1;
+	}
+
+	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);
 
@@ -431,7 +448,7 @@ 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))