futex: Fix OWNER_DEAD fixup

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 <geert@linux-m68k.org>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Link: http://lkml.kernel.org/r/20180122103947.GD2228@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/futex.c b/kernel/futex.c
index 8c5424dd59244f0a7f95dea339048f3bdfffaaba..7f719d11090810622ff010c0b8adc3fe954c478d 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2311,9 +2311,6 @@ static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
        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;