[PATCH v2] s390/debug: Do not register views for failed static debug areas

[Mikhail Zaslonko <zaslonko@linux.ibm.com>]

__REGISTER_STATIC_DEBUG_INFO() calls debug_register_view()
unconditionally, even when debug_register_static() has failed. In that
case _debug_register() was never reached and id->debugfs_root_entry is
still NULL, so debugfs_create_file() places the view file in the debugfs
root directory. For sclp_err this leaves a /sys/kernel/debug/hex_ascii
file with nothing to indicate which debug log it belongs to.

debug_register_static() is not exported and the macro is its only
caller, so let it return an error code and skip the view registration
when it fails. No debugfs files are created for such an area then.

Reproduce by booting with s390dbf=sclp_err::100000000. The sclp_err
registration fails, no s390dbf/sclp_err/ directory is created, and a
hex_ascii file appears in the debugfs root instead.

Fixes: d72541f94512 ("s390/debug: add early tracing support")
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
---
v2:
- Resend as regular patch, no functional changes since RFC

 arch/s390/include/asm/debug.h |  8 ++++++--
 arch/s390/kernel/debug.c      | 12 +++++++++---
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/s390/include/asm/debug.h b/arch/s390/include/asm/debug.h
index 39d484c59774..ad438d6352c8 100644
--- a/arch/s390/include/asm/debug.h
+++ b/arch/s390/include/asm/debug.h
@@ -460,7 +460,11 @@ static int VNAME(var, active_entries)[EARLY_AREAS] __initdata
 #define __REGISTER_STATIC_DEBUG_INFO(var, name, pages, areas, view)	\
 static int __init VNAME(var, reg)(void)					\
 {									\
-	debug_register_static(&var, (pages), (areas));			\
+	int rc;								\
+									\
+	rc = debug_register_static(&var, (pages), (areas));		\
+	if (rc)								\
+		return rc;						\
 	debug_register_view(&var, (view));				\
 	return 0;							\
 }									\
@@ -493,7 +497,7 @@ static debug_info_t __refdata var =					\
 static debug_info_t __used __section(".s390dbf_info") *VNAME(var, info) = &var; \
 __REGISTER_STATIC_DEBUG_INFO(var, name, pages, nr_areas, view)
 
-void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas);
+int debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas);
 
 #endif /* MODULE */
 
diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index b5bf8284dbfc..c6f3a55fcfa9 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -950,8 +950,12 @@ EXPORT_SYMBOL(debug_register);
  *
  * Note: This function is called automatically via an initcall generated by
  *	 DEFINE_STATIC_DEBUG_INFO.
+ *
+ * Return:
+ * - 0 on success
+ * - negative error code on failure
  */
-void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
+int debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
 {
 	unsigned long flags;
 	debug_info_t *copy;
@@ -959,7 +963,7 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
 	if (!initialized) {
 		pr_err("Tried to register debug feature %s too early\n",
 		       id->name);
-		return;
+		return -EINVAL;
 	}
 
 	debug_get_param(id->name, &id->level, &pages_per_area, false);
@@ -975,7 +979,7 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
 		id->active_entries = NULL;
 		raw_spin_unlock_irqrestore(&id->lock, flags);
 
-		return;
+		return -ENOMEM;
 	}
 
 	/* Replace static trace area with dynamic copy. */
@@ -993,6 +997,8 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
 	mutex_lock(&debug_mutex);
 	_debug_register(id);
 	mutex_unlock(&debug_mutex);
+
+	return 0;
 }
 
 /* Remove debugfs entries. */
-- 
2.55.0