kmemleak: always register debugfs file

If kmemleak built in to the kernel, but is disabled by default, the
debugfs file is never registered.  Because of this, it is not possible
to find out if the kernel is built with kmemleak support by checking for
the presence of this file.  To allow this, always register the file.

After this patch, if the file doesn't exist, kmemleak is not available
in the kernel.  If writing "scan" or any other value than "clear" to
this file results in EBUSY, then kmemleak is available but is disabled
by default and can be activated via the kernel command line.

Catalin: "that's also consistent with a late disabling of kmemleak when
the debugfs entry sticks around."

Link: http://lkml.kernel.org/r/20180824131220.19176-1-vincent.whitchurch@axis.com
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 9a085d525bbce1bd4aabb4599236d2874c964850..17dd883198aeab0dccebe762a6b432dad2f14c9d 100644 (file)
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -2097,6 +2097,11 @@ static int __init kmemleak_late_init(void)
 
        kmemleak_initialized = 1;
 
+       dentry = debugfs_create_file("kmemleak", 0644, NULL, NULL,
+                                    &kmemleak_fops);
+       if (!dentry)
+               pr_warn("Failed to create the debugfs kmemleak file\n");
+
        if (kmemleak_error) {
                /*
                 * Some error occurred and kmemleak was disabled. There is a
@@ -2108,10 +2113,6 @@ static int __init kmemleak_late_init(void)
                return -ENOMEM;
        }
 
-       dentry = debugfs_create_file("kmemleak", 0644, NULL, NULL,
-                                    &kmemleak_fops);
-       if (!dentry)
-               pr_warn("Failed to create the debugfs kmemleak file\n");
        mutex_lock(&scan_mutex);
        start_scan_thread();
        mutex_unlock(&scan_mutex);