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.n... 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 199e63c5b612..70ad21bbb1d5 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2248,10 +2248,6 @@ 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: * @@ -2309,6 +2305,9 @@ 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;