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Subject[PATCH 005/109] mm: use do_futex() instead of sys_futex() in mm_release()
Date
sys_futex() is a wrapper to do_futex() which does not modify any
values here:

- uaddr, val and val3 are kept the same

- op is masked with FUTEX_CMD_MASK, but is always set to FUTEX_WAKE.
Therefore, val2 is always 0.

- as utime is set to NULL, *timeout is NULL

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
---
include/linux/futex.h | 13 ++++++++++---
kernel/fork.c | 4 ++--
2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/futex.h b/include/linux/futex.h
index c0fb9a24bbd2..821ae502d3d8 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -9,9 +9,6 @@ struct inode;
struct mm_struct;
struct task_struct;

-long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
- u32 __user *uaddr2, u32 val2, u32 val3);
-
extern int
handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi);

@@ -55,6 +52,9 @@ union futex_key {

#ifdef CONFIG_FUTEX
extern void exit_robust_list(struct task_struct *curr);
+
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+ u32 __user *uaddr2, u32 val2, u32 val3);
#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
#define futex_cmpxchg_enabled 1
#else
@@ -64,6 +64,13 @@ extern int futex_cmpxchg_enabled;
static inline void exit_robust_list(struct task_struct *curr)
{
}
+
+static inline long do_futex(u32 __user *uaddr, int op, u32 val,
+ ktime_t *timeout, u32 __user *uaddr2,
+ u32 val2, u32 val3)
+{
+ return -EINVAL;
+}
#endif

#ifdef CONFIG_FUTEX_PI
diff --git a/kernel/fork.c b/kernel/fork.c
index e5d9d405ae4e..b1e031aac9db 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1198,8 +1198,8 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
* not set up a proper pointer then tough luck.
*/
put_user(0, tsk->clear_child_tid);
- sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
- 1, NULL, NULL, 0);
+ do_futex(tsk->clear_child_tid, FUTEX_WAKE,
+ 1, NULL, NULL, 0, 0);
}
tsk->clear_child_tid = NULL;
}
--
2.16.3
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