The following commit has been merged in the linux branch: commit 11df6dddcbc38affb7473aad3d962baf8414a947 Author: Thomas Gleixner tglx@linutronix.de Date: Wed Oct 28 20:26:48 2009 +0100

futex: Fix spurious wakeup for requeue_pi really

The requeue_pi path doesn't use unqueue_me() (and the racy lock_ptr == NULL test) nor does it use the wake_list of futex_wake() which where the reason for commit 41890f2 (futex: Handle spurious wake up)

See debugging discussing on LKML Message-ID: 4AD4080C.20703@us.ibm.com

The changes in this fix to the wait_requeue_pi path were considered to be a likely unecessary, but harmless safety net. But it turns out that due to the fact that for unknown $@#!*( reasons EWOULDBLOCK is defined as EAGAIN we built an endless loop in the code path which returns correctly EWOULDBLOCK.

Spurious wakeups in wait_requeue_pi code path are unlikely so we do the easy solution and return EWOULDBLOCK^WEAGAIN to user space and let it deal with the spurious wakeup.

Cc: Darren Hart dvhltc@us.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Eric Dumazet eric.dumazet@gmail.com Cc: John Stultz johnstul@linux.vnet.ibm.com Cc: Dinakar Guniguntala dino@in.ibm.com LKML-Reference: 4AE23C74.1090502@us.ibm.com Cc: stable@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de

diff --git a/kernel/futex.c b/kernel/futex.c index 642f3bb..fb65e82 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2127,7 +2127,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, plist_del(&q->list, &q->list.plist);

/* Handle spurious wakeups gracefully */ - ret = -EAGAIN; + ret = -EWOULDBLOCK; if (timeout && !timeout->task) ret = -ETIMEDOUT; else if (signal_pending(current)) @@ -2208,7 +2208,6 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, debug_rt_mutex_init_waiter(&rt_waiter); rt_waiter.task = NULL;

-retry: key2 = FUTEX_KEY_INIT; ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE); if (unlikely(ret != 0)) @@ -2303,9 +2302,6 @@ out_put_keys: out_key2: put_futex_key(fshared, &key2);

- /* Spurious wakeup ? */ - if (ret == -EAGAIN) - goto retry; out: if (to) { hrtimer_cancel(&to->timer);