[PATCH 5/5] compat_ioctl: do not hold BKL in handlers

[Arnd Bergmann <arnd@arndb.de>]

We have always called ioctl conversion handlers under the big
kernel lock, although that is generally not necessary. In particular
it is not needed for conversion of data structures and for calling
sys_ioctl or do_vfs_ioctl, which will get the BKL again if needed.

Handlers doing more than those two have been moved out, so we
can kill off the BKL from compat_sys_ioctl. This may significantly
improve latencies with 32 bit applications, and it avoids a common
scenario where a thread acquires the BKL twice.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 fs/compat_ioctl.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index 5d800aa..86e6c75 100644
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -2637,9 +2637,7 @@ asmlinkage long compat_sys_ioctl(unsigned int fd, unsigned int cmd,
 
  found_handler:
 	if (t->handler) {
-		lock_kernel();
 		error = t->handler(fd, cmd, arg, filp);
-		unlock_kernel();
 		goto out_fput;
 	}
 
-- 
1.6.3.3