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futex: Fix spurious wakeup for requeue_pi really

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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>
This commit is contained in:
Thomas Gleixner 2009-10-28 20:26:48 +01:00
parent 89061d3d58
commit 11df6dddcb
1 changed files with 1 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
kernel/futex.c
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@ -2127,7 +2127,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
plist_del(&q->list, &q->list.plist); plist_del(&q->list, &q->list.plist);
/* Handle spurious wakeups gracefully */ /* Handle spurious wakeups gracefully */
ret = -EAGAIN; ret = -EWOULDBLOCK;
if (timeout && !timeout->task) if (timeout && !timeout->task)
ret = -ETIMEDOUT; ret = -ETIMEDOUT;
else if (signal_pending(current)) 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); debug_rt_mutex_init_waiter(&rt_waiter);
rt_waiter.task = NULL; rt_waiter.task = NULL;
retry:
key2 = FUTEX_KEY_INIT; key2 = FUTEX_KEY_INIT;
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE); ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0)) if (unlikely(ret != 0))
@ -2303,9 +2302,6 @@ out_put_keys:
out_key2: out_key2:
put_futex_key(fshared, &key2); put_futex_key(fshared, &key2);
/* Spurious wakeup ? */
if (ret == -EAGAIN)
goto retry;
out: out:
if (to) { if (to) {
hrtimer_cancel(&to->timer); hrtimer_cancel(&to->timer);