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Subject[PATCH 4.9.257 1/1] futex: Fix OWNER_DEAD fixup
Date
From: Peter Zijlstra <peterz@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 <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>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
---
kernel/futex.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 83db5787c67e..7cb2baa9446a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2283,10 +2283,6 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,

oldowner = pi_state->owner;

- /* Owner died? */
- if (!pi_state->owner)
- newtid |= FUTEX_OWNER_DIED;
-
/*
* We are here because either:
*
@@ -2344,6 +2340,9 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
}

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;
--
2.25.4
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