dynamic_debug: allow to work if debugfs is disabled

With the realization that having debugfs enabled on "production" systems
is generally not a good idea, debugfs is being disabled from more and
more platforms over time.  However, the functionality of dynamic
debugging still is needed at times, and since it relies on debugfs for
its user api, having debugfs disabled also forces dynamic debug to be
disabled.

To get around this, also create the "control" file for dynamic_debug in
procfs.  This allows people turn on debugging as needed at runtime for
individual driverfs and subsystems.

Reported-by: many different companies
Cc: Jason Baron <jbaron@akamai.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200210211142.GB1373304@kroah.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 5 deletions

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c60409138e13..aae17d9522e5 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -876,6 +876,14 @@ static const struct file_operations ddebug_proc_fops = {
 	.write = ddebug_proc_write
 };
 
+static const struct proc_ops proc_fops = {
+	.proc_open = ddebug_proc_open,
+	.proc_read = seq_read,
+	.proc_lseek = seq_lseek,
+	.proc_release = seq_release_private,
+	.proc_write = ddebug_proc_write
+};
+
 /*
  * Allocate a new ddebug_table for the given module
  * and add it to the global list.
@@ -991,15 +999,25 @@ static void ddebug_remove_all_tables(void)
 
 static __initdata int ddebug_init_success;
 
-static int __init dynamic_debug_init_debugfs(void)
+static int __init dynamic_debug_init_control(void)
 {
-	struct dentry *dir;
+	struct proc_dir_entry *procfs_dir;
+	struct dentry *debugfs_dir;
 
 	if (!ddebug_init_success)
 		return -ENODEV;
 
-	dir = debugfs_create_dir("dynamic_debug", NULL);
-	debugfs_create_file("control", 0644, dir, NULL, &ddebug_proc_fops);
+	/* Create the control file in debugfs if it is enabled */
+	if (debugfs_initialized()) {
+		debugfs_dir = debugfs_create_dir("dynamic_debug", NULL);
+		debugfs_create_file("control", 0644, debugfs_dir, NULL,
+				    &ddebug_proc_fops);
+	}
+
+	/* Also create the control file in procfs */
+	procfs_dir = proc_mkdir("dynamic_debug", NULL);
+	if (procfs_dir)
+		proc_create("control", 0644, procfs_dir, &proc_fops);
 
 	return 0;
 }
@@ -1077,4 +1095,4 @@ out_err:
 early_initcall(dynamic_debug_init);
 
 /* Debugfs setup must be done later */
-fs_initcall(dynamic_debug_init_debugfs);
+fs_initcall(dynamic_debug_init_control);