>From d6b2a11dab074c1a28b497525a61dc448d7073d2 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 3 Jun 2014 12:27:07 +0000 Subject: [PATCH 3/4] futex: Always cleanup owner tid in unlock_pi If the owner died bit is set at futex_unlock_pi, we currently do not cleanup the user space futex. So the owner TID of the current owner (the unlocker) persists. That's observable inconsistant state, especially when the ownership of the pi state got transferred. Clean it up unconditionally. Backport to 2.6.32: conflicts: kernel/futex.c Signed-off-by: Thomas Gleixner Signed-off-by: John Johansen Cc: Kees Cook Cc: Will Drewry Cc: Darren Hart Cc: stable@...r.kernel.org --- kernel/futex.c | 43 +++++++++++++++++++------------------------ 1 file changed, 19 insertions(+), 24 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 179f08f..7be53af 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -811,6 +811,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) struct task_struct *new_owner; struct futex_pi_state *pi_state = this->pi_state; u32 curval, newval; + int ret = 0; if (!pi_state) return -EINVAL; @@ -835,25 +836,20 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) new_owner = this->task; /* - * We pass it to the next owner. (The WAITERS bit is always - * kept enabled while there is PI state around. We must also - * preserve the owner died bit.) + * We pass it to the next owner. The WAITERS bit is always + * kept enabled while there is PI state around. We cleanup the + * owner died bit, because we are the owner. */ - if (!(uval & FUTEX_OWNER_DIED)) { - int ret = 0; - - newval = FUTEX_WAITERS | task_pid_vnr(new_owner); - - curval = cmpxchg_futex_value_locked(uaddr, uval, newval); + newval = FUTEX_WAITERS | task_pid_vnr(new_owner); - if (curval == -EFAULT) - ret = -EFAULT; - else if (curval != uval) - ret = -EINVAL; - if (ret) { - spin_unlock(&pi_state->pi_mutex.wait_lock); - return ret; - } + curval = cmpxchg_futex_value_locked(uaddr, uval, newval); + if (curval == -EFAULT) + ret = -EFAULT; + else if (curval != uval) + ret = -EINVAL; + if (ret) { + spin_unlock(&pi_state->pi_mutex.wait_lock); + return ret; } spin_lock_irq(&pi_state->owner->pi_lock); @@ -2107,9 +2103,10 @@ retry: /* * To avoid races, try to do the TID -> 0 atomic transition * again. If it succeeds then we can return without waking - * anyone else up: + * anyone else up. We only try this if neither the waiters nor + * the owner died bit are set. */ - if (!(uval & FUTEX_OWNER_DIED)) + if (!(uval & ~FUTEX_TID_MASK)) uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0); @@ -2144,11 +2141,9 @@ retry: /* * No waiters - kernel unlocks the futex: */ - if (!(uval & FUTEX_OWNER_DIED)) { - ret = unlock_futex_pi(uaddr, uval); - if (ret == -EFAULT) - goto pi_faulted; - } + ret = unlock_futex_pi(uaddr, uval); + if (ret == -EFAULT) + goto pi_faulted; out_unlock: spin_unlock(&hb->lock); -- 2.0.0