From d58e6576b0deec6f0b9ff8450fe282da18c50883 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 13 Oct 2009 20:40:43 +0200 Subject: futex: Handle spurious wake up The futex code does not handle spurious wake up in futex_wait and futex_wait_requeue_pi. The code assumes that any wake up which was not caused by futex_wake / requeue or by a timeout was caused by a signal wake up and returns one of the syscall restart error codes. In case of a spurious wake up the signal delivery code which deals with the restart error codes is not invoked and we return that error code to user space. That causes applications which actually check the return codes to fail. Blaise reported that on preempt-rt a python test program run into a exception trap. -rt exposed that due to a built in spurious wake up accelerator :) Solve this by checking signal_pending(current) in the wake up path and handle the spurious wake up case w/o returning to user space. Reported-by: Blaise Gassend Debugged-by: Darren Hart Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: stable@kernel.org LKML-Reference: --- kernel/futex.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'kernel/futex.c') diff --git a/kernel/futex.c b/kernel/futex.c index 4949d336d88d..5c88839bd993 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1791,6 +1791,7 @@ static int futex_wait(u32 __user *uaddr, int fshared, current->timer_slack_ns); } +retry: /* Prepare to wait on uaddr. */ ret = futex_wait_setup(uaddr, val, fshared, &q, &hb); if (ret) @@ -1808,9 +1809,14 @@ static int futex_wait(u32 __user *uaddr, int fshared, goto out_put_key; /* - * We expect signal_pending(current), but another thread may - * have handled it for us already. + * We expect signal_pending(current), but we might be the + * victim of a spurious wakeup as well. */ + if (!signal_pending(current)) { + put_futex_key(fshared, &q.key); + goto retry; + } + ret = -ERESTARTSYS; if (!abs_time) goto out_put_key; @@ -2118,9 +2124,11 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, */ plist_del(&q->list, &q->list.plist); + /* Handle spurious wakeups gracefully */ + ret = -EAGAIN; if (timeout && !timeout->task) ret = -ETIMEDOUT; - else + else if (signal_pending(current)) ret = -ERESTARTNOINTR; } return ret; @@ -2198,6 +2206,7 @@ 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)) @@ -2292,6 +2301,9 @@ 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 From 2bc872036e1c5948b5b02942810bbdd8dbdb9812 Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Wed, 14 Oct 2009 10:12:39 -0700 Subject: futex: Check for NULL keys in match_futex If userspace tries to perform a requeue_pi on a non-requeue_pi waiter, it will find the futex_q->requeue_pi_key to be NULL and OOPS. Check for NULL in match_futex() instead of doing explicit NULL pointer checks on all call sites. While match_futex(NULL, NULL) returning false is a little odd, it's still correct as we expect valid key references. Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Ingo Molnar CC: Eric Dumazet CC: Dinakar Guniguntala CC: John Stultz Cc: stable@kernel.org LKML-Reference: <4AD60687.10306@us.ibm.com> Signed-off-by: Thomas Gleixner --- kernel/futex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/futex.c') diff --git a/kernel/futex.c b/kernel/futex.c index 5c88839bd993..06938e560ac9 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -150,7 +150,8 @@ static struct futex_hash_bucket *hash_futex(union futex_key *key) */ static inline int match_futex(union futex_key *key1, union futex_key *key2) { - return (key1->both.word == key2->both.word + return (key1 && key2 + && key1->both.word == key2->both.word && key1->both.ptr == key2->both.ptr && key1->both.offset == key2->both.offset); } -- cgit v1.2.3 From 89061d3d58e1f0742139605dc6a7950aa1ecc019 Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Thu, 15 Oct 2009 15:30:48 -0700 Subject: futex: Move drop_futex_key_refs out of spinlock'ed region When requeuing tasks from one futex to another, the reference held by the requeued task to the original futex location needs to be dropped eventually. Dropping the reference may ultimately lead to a call to "iput_final" and subsequently call into filesystem- specific code - which may be non-atomic. It is therefore safer to defer this drop operation until after the futex_hash_bucket spinlock has been dropped. Originally-From: Helge Bahmann Signed-off-by: Darren Hart Cc: Cc: Peter Zijlstra Cc: Eric Dumazet Cc: Dinakar Guniguntala Cc: John Stultz Cc: Sven-Thorsten Dietrich Cc: John Kacur LKML-Reference: <4AD7A298.5040802@us.ibm.com> Signed-off-by: Ingo Molnar --- kernel/futex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/futex.c') diff --git a/kernel/futex.c b/kernel/futex.c index 06938e560ac9..642f3bbaacc7 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1029,7 +1029,6 @@ static inline void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, struct futex_hash_bucket *hb) { - drop_futex_key_refs(&q->key); get_futex_key_refs(key); q->key = *key; @@ -1227,6 +1226,7 @@ retry_private: */ if (ret == 1) { WARN_ON(pi_state); + drop_count++; task_count++; ret = get_futex_value_locked(&curval2, uaddr2); if (!ret) @@ -1305,6 +1305,7 @@ retry_private: if (ret == 1) { /* We got the lock. */ requeue_pi_wake_futex(this, &key2, hb2); + drop_count++; continue; } else if (ret) { /* -EDEADLK */ -- cgit v1.2.3