Commit a97cb0e7 authored Jan 22, 2018 by Peter Zijlstra Committed by Ingo Molnar Jan 24, 2018

futex: Fix OWNER_DEAD fixup



Both Geert and DaveJ reported that the recent futex commit:

  c1e2f0ea ("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: c1e2f0ea ("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>

parent 1f07476e

kernel/futex.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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;

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