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Commit 2de0db99 authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

mm: use do_futex() instead of sys_futex() in mm_release() 

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent 6b27aef0

include/linux/futex.h

+10 −3
Original line number Diff line number Diff line
@@ -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

kernel/fork.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

	}