[PATCH] staging/android: sync_debug: unproxify debugfs files' fops

From: Nicolai Stange
Date: Fri May 27 2016 - 14:04:12 EST

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
Fixes: a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs
Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
Applicable to linux-next-20160527.
x86_64 allmodconfig build succeeds w/o any new warnings.

Related discussion can be found here:

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;