[PATCH v4] cxl/core: Create einj_types when EINJ becomes available

[Yongxin Yang]

From: Yang Yongxin <yangyongxin@xxxxxxxxxx>

The einj_types file under the CXL debugfs directory is never created when
cxl_core is built in.

cxl_core_init() runs at subsys_initcall level, while EINJ registers itself
from einj_init() at device_initcall level. With cxl_core built in, the
einj_cxl_is_initialized() check in cxl_core_init() therefore always sees
false and the debugfs_create_file("einj_types") call below it is never
reached, so users have no way to discover which CXL error types the
platform supports from debugfs. When cxl_core is a module, module
dependencies make sure it is loaded after EINJ is up, and the file is
created.

Create the file from every point that can tell EINJ is up. cxl_core_init()
covers cxl_core being a module loaded after EINJ has been initialized. The
cxl_acpi_probe() hook covers cxl_core being built in while cxl_acpi is a
module, and is the only hook that can work on RCH/RCD hierarchies, where
the single dport is added by the ACPI probe itself, too early to help. The
dport probe path covers the built-in virtual host case, where the dport
added from the memdev probe is the only hook reached after einj_init().

The dport probe path can run concurrently for different parent ports, each
holding only its own device lock, so serialize the check and the create to
avoid a duplicate debugfs_create_file() attempt that would only fail with
-EEXIST. Reset the cached dentry in cxl_core_exit() so that reloading
cxl_core starts from a clean state.

Fixes: 8039804cfa73 ("cxl/core: Add CXL EINJ debugfs files")
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/de14c4ef-e3d8-432f-9ce8-87c468d6d2ad@xxxxxxx/
Link: https://lore.kernel.org/all/7a22cc6a-deba-40e6-8033-97d1234420ba@xxxxxxx/
Reviewed-by: Ben Cheatham <benjamin.cheatham@xxxxxxx>
Signed-off-by: Yang Yongxin <yangyongxin@xxxxxxxxxx>
---
Changes in v4:
- Scope the problem statement to the built-in case: the file is only never
  created when cxl_core is built in, the module dependencies take care of the
  ordering otherwise.
- Replace the "no dport is ever added" rationale with the RCH/RCD case, in
  the changelog and in the cxl_acpi_probe() comment: a system without any
  dport cannot do error injection at all, so the file is useless there. On
  RCH/RCD hierarchies the only dport comes from the ACPI probe, so this hook
  is the one that matters.

 drivers/cxl/acpi.c      |  9 +++++++++
 drivers/cxl/core/port.c | 41 +++++++++++++++++++++++++++++++++++------
 drivers/cxl/cxl.h       |  2 ++
 3 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 3b818adbd38b..ca7741203740 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -958,6 +958,15 @@ static int cxl_acpi_probe(struct platform_device *pdev)
 	if (rc < 0)
 		return rc;
 
+	/*
+	 * Create einj_types from here as well: with cxl_core built in,
+	 * cxl_core_init() runs before EINJ is up, so when cxl_acpi is a module
+	 * loaded afterwards this is the only hook that can create the file,
+	 * including on RCH/RCD hierarchies, where the single dport is added by
+	 * this probe itself and cannot help.
+	 */
+	cxl_debugfs_einj_add_types();
+
 	/* In case PCI is scanned before ACPI re-trigger memdev attach */
 	cxl_bus_rescan();
 	return 0;
diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 625e4aa427db..76ac612b514c 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -802,6 +802,35 @@ static int cxl_dport_setup_regs(struct device *host, struct cxl_dport *dport,
 
 DEFINE_SHOW_ATTRIBUTE(einj_cxl_available_error_type);
 
+static struct dentry *cxl_debugfs;
+static struct dentry *einj_types_dentry;
+
+/*
+ * einj_types can only be created once EINJ is up, and no single hook is
+ * reached after that point in every configuration:
+ *
+ *  - cxl_core_init() runs at subsys_initcall level and cxl_acpi_probe() at
+ *    subsys_initcall_sync level, so both create the file when cxl_core and
+ *    cxl_acpi are modules loaded after EINJ has been initialized;
+ *  - when EINJ is built in, einj_init() runs at device_initcall level, so
+ *    both of them are too early and the only hook left is the dport added
+ *    from the memdev probe.
+ *
+ * The dport probe path can run concurrently for different parent ports, each
+ * holding only its own device lock, so the check and the create need to be
+ * serialized to avoid a duplicate debugfs_create_file() attempt.
+ */
+static DEFINE_MUTEX(einj_types_lock);
+void cxl_debugfs_einj_add_types(void)
+{
+	guard(mutex)(&einj_types_lock);
+	if (cxl_debugfs && !einj_types_dentry && einj_cxl_is_initialized())
+		einj_types_dentry = debugfs_create_file("einj_types", 0400,
+							cxl_debugfs, NULL,
+							&einj_cxl_available_error_type_fops);
+}
+EXPORT_SYMBOL_FOR_MODULES(cxl_debugfs_einj_add_types, "cxl_acpi");
+
 static int cxl_einj_inject(void *data, u64 type)
 {
 	struct cxl_dport *dport = data;
@@ -822,6 +851,8 @@ static void cxl_debugfs_create_dport_dir(struct cxl_dport *dport)
 	if (!einj_cxl_is_initialized())
 		return;
 
+	cxl_debugfs_einj_add_types();
+
 	/*
 	 * Protocol error injection is only available for CXL 2.0+ root ports
 	 * and CXL 1.1 downstream ports
@@ -2501,8 +2532,6 @@ const struct bus_type cxl_bus_type = {
 };
 EXPORT_SYMBOL_NS_GPL(cxl_bus_type, "CXL");
 
-static struct dentry *cxl_debugfs;
-
 struct dentry *cxl_debugfs_create_dir(const char *dir)
 {
 	return debugfs_create_dir(dir, cxl_debugfs);
@@ -2515,10 +2544,6 @@ static __init int cxl_core_init(void)
 
 	cxl_debugfs = debugfs_create_dir("cxl", NULL);
 
-	if (einj_cxl_is_initialized())
-		debugfs_create_file("einj_types", 0400, cxl_debugfs, NULL,
-				    &einj_cxl_available_error_type_fops);
-
 	cxl_mbox_init();
 
 	rc = cxl_memdev_init();
@@ -2541,6 +2566,8 @@ static __init int cxl_core_init(void)
 
 	cxl_ras_init();
 
+	cxl_debugfs_einj_add_types();
+
 	return 0;
 
 err_region:
@@ -2560,6 +2587,8 @@ static void cxl_core_exit(void)
 	destroy_workqueue(cxl_bus_wq);
 	cxl_memdev_exit();
 	debugfs_remove_recursive(cxl_debugfs);
+	cxl_debugfs = NULL;
+	einj_types_dentry = NULL;
 }
 
 subsys_initcall(cxl_core_init);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index cab8ce39f465..b9245261ee39 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -926,4 +926,6 @@ struct cxl_dport *devm_cxl_add_dport_by_dev(struct cxl_port *port,
 
 u16 cxl_gpf_get_dvsec(struct device *dev);
 
+void cxl_debugfs_einj_add_types(void);
+
 #endif /* __CXL_H__ */
-- 
2.25.1