4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <pet...@infradead.org>

commit a97cb0e7b3f4c6297fd857055ae8e895f402f501 upstream.

Both Geert and DaveJ reported that the recent futex commit:

  c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")

introduced a problem with setting OWNER_DEAD. We set the bit on an
uninitialized variable and then entirely optimize it away as a
dead-store.

Move the setting of the bit to where it is more useful.

Reported-by: Geert Uytterhoeven <ge...@linux-m68k.org>
Reported-by: Dave Jones <da...@codemonkey.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paul E. McKenney <paul...@us.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Link: 
http://lkml.kernel.org/r/20180122103947.gd2...@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Cc: Ozkan Sezer <seze...@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/futex.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2311,9 +2311,6 @@ static int fixup_pi_state_owner(u32 __us
        raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
        oldowner = pi_state->owner;
-       /* Owner died? */
-       if (!pi_state->owner)
-               newtid |= FUTEX_OWNER_DIED;
 
        /*
         * We are here because either:
@@ -2374,6 +2371,9 @@ retry:
        }
 
        newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+       /* Owner died? */
+       if (!pi_state->owner)
+               newtid |= FUTEX_OWNER_DIED;
 
        if (get_futex_value_locked(&uval, uaddr))
                goto handle_fault;


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