From fc7df048bf93e52c04f4c39104a5a388b73725b8 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 28 Oct 2009 20:26:48 +0100 Subject: futex: Fix spurious wakeup for requeue_pi really commit 11df6dddcbc38affb7473aad3d962baf8414a947 upstream. 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 Cc: Peter Zijlstra Cc: Eric Dumazet Cc: John Stultz Cc: Dinakar Guniguntala LKML-Reference: <4AE23C74.1090502@us.ibm.com> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman --- kernel/futex.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index f435af120a67..c0a020fcc246 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2103,7 +2103,7 @@ 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)) @@ -2184,7 +2184,6 @@ 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)) @@ -2282,9 +2281,6 @@ out_put_keys: out_key2: put_futex_key(fshared, &key2); - /* Spurious wakeup ? */ - if (ret == -EAGAIN) - goto retry; out: if (to) { hrtimer_cancel(&to->timer); -- cgit v1.2.3