Since commit 49d200deaa68 ("debugfs: prevent access to removed files'
private data"), a debugfs file's file_operations methods get proxied
through lifetime aware wrappers.

However, only a certain subset of the file_operations members is supported
by debugfs and ->compat_ioctl isn't among them -- it appears to be NULL
from the VFS layer's perspective.

This behaviour breaks the /sys/kernel/debug/sync/sw_sync file introduced
concurrently with commit a44eb74cd413 ("staging/android: move SW_SYNC_USER
to a debugfs file").

Since that file never gets removed, there is no file removal race and thus,
a lifetime checking proxy isn't needed.

Avoid the proxying for /sys/kernel/debug/sync/sw_sync by creating it via
debugfs_create_file_unsafe() rather than debugfs_create_file().
For consistency, do the same for /sys/kernel/debug/sync/info.

Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private
                      data")
Fixes: a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs
                      file")
Signed-off-by: Nicolai Stange <nicsta...@gmail.com>
---
 Applicable to linux-next-20160527.
 x86_64 allmodconfig build succeeds w/o any new warnings.

 Related discussion can be found here:
 http://lkml.kernel.org/g/878tz22peb....@gmail.com

 drivers/staging/android/sync_debug.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/android/sync_debug.c 
b/drivers/staging/android/sync_debug.c
index 5f57499..1197f9e 100644
--- a/drivers/staging/android/sync_debug.c
+++ b/drivers/staging/android/sync_debug.c
@@ -326,9 +326,15 @@ static __init int sync_debugfs_init(void)
 {
        dbgfs = debugfs_create_dir("sync", NULL);
 
-       debugfs_create_file("info", 0444, dbgfs, NULL, &sync_info_debugfs_fops);
-       debugfs_create_file("sw_sync", 0644, dbgfs, NULL,
-                           &sw_sync_debugfs_fops);
+       /*
+        * The debugfs files won't ever get removed and thus, there is
+        * no need to protect it against removal races. The use of
+        * debugfs_create_file_unsafe() is actually safe here.
+        */
+       debugfs_create_file_unsafe("info", 0444, dbgfs, NULL,
+                                  &sync_info_debugfs_fops);
+       debugfs_create_file_unsafe("sw_sync", 0644, dbgfs, NULL,
+                                  &sw_sync_debugfs_fops);
 
        return 0;
 }
-- 
2.8.2

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