[PATCH] pi-futex: robust-futex exit
Fix robust PI-futexes to be properly unlocked on unexpected exit.
For this to work the kernel has to know whether a futex is a PI or a
non-PI one, because the semantics are different. Since the space in
relevant glibc data structures is extremely scarce, the best solution is
to encode the 'PI' information in bit 0 of the robust list pointer.
Existing (non-PI) glibc robust futexes have this bit always zero, so the
ABI is kept. New glibc with PI-robust-futexes will set this bit.
Further fixes from Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/futex.c b/kernel/futex.c
index f59003b..dda2049 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -495,10 +495,13 @@
}
/*
- * We are the first waiter - try to look up the real owner and
- * attach the new pi_state to it:
+ * We are the first waiter - try to look up the real owner and attach
+ * the new pi_state to it, but bail out when the owner died bit is set
+ * and TID = 0:
*/
pid = uval & FUTEX_TID_MASK;
+ if (!pid && (uval & FUTEX_OWNER_DIED))
+ return -ESRCH;
p = futex_find_get_task(pid);
if (!p)
return -ESRCH;
@@ -579,16 +582,17 @@
* kept enabled while there is PI state around. We must also
* preserve the owner died bit.)
*/
- newval = (uval & FUTEX_OWNER_DIED) | FUTEX_WAITERS | new_owner->pid;
+ if (!(uval & FUTEX_OWNER_DIED)) {
+ newval = FUTEX_WAITERS | new_owner->pid;
- inc_preempt_count();
- curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
- dec_preempt_count();
-
- if (curval == -EFAULT)
- return -EFAULT;
- if (curval != uval)
- return -EINVAL;
+ inc_preempt_count();
+ curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
+ dec_preempt_count();
+ if (curval == -EFAULT)
+ return -EFAULT;
+ if (curval != uval)
+ return -EINVAL;
+ }
spin_lock_irq(&pi_state->owner->pi_lock);
WARN_ON(list_empty(&pi_state->list));
@@ -1443,9 +1447,11 @@
* again. If it succeeds then we can return without waking
* anyone else up:
*/
- inc_preempt_count();
- uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
- dec_preempt_count();
+ if (!(uval & FUTEX_OWNER_DIED)) {
+ inc_preempt_count();
+ uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
+ dec_preempt_count();
+ }
if (unlikely(uval == -EFAULT))
goto pi_faulted;
@@ -1478,9 +1484,11 @@
/*
* No waiters - kernel unlocks the futex:
*/
- ret = unlock_futex_pi(uaddr, uval);
- if (ret == -EFAULT)
- goto pi_faulted;
+ if (!(uval & FUTEX_OWNER_DIED)) {
+ ret = unlock_futex_pi(uaddr, uval);
+ if (ret == -EFAULT)
+ goto pi_faulted;
+ }
out_unlock:
spin_unlock(&hb->lock);
@@ -1699,9 +1707,9 @@
* Process a futex-list entry, check whether it's owned by the
* dying task, and do notification if so:
*/
-int handle_futex_death(u32 __user *uaddr, struct task_struct *curr)
+int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
{
- u32 uval, nval;
+ u32 uval, nval, mval;
retry:
if (get_user(uval, uaddr))
@@ -1718,21 +1726,45 @@
* thread-death.) The rest of the cleanup is done in
* userspace.
*/
- nval = futex_atomic_cmpxchg_inatomic(uaddr, uval,
- uval | FUTEX_OWNER_DIED);
+ mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
+ nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
+
if (nval == -EFAULT)
return -1;
if (nval != uval)
goto retry;
- if (uval & FUTEX_WAITERS)
- futex_wake(uaddr, 1);
+ /*
+ * Wake robust non-PI futexes here. The wakeup of
+ * PI futexes happens in exit_pi_state():
+ */
+ if (!pi) {
+ if (uval & FUTEX_WAITERS)
+ futex_wake(uaddr, 1);
+ }
}
return 0;
}
/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int fetch_robust_entry(struct robust_list __user **entry,
+ struct robust_list __user **head, int *pi)
+{
+ unsigned long uentry;
+
+ if (get_user(uentry, (unsigned long *)head))
+ return -EFAULT;
+
+ *entry = (void *)(uentry & ~1UL);
+ *pi = uentry & 1;
+
+ return 0;
+}
+
+/*
* Walk curr->robust_list (very carefully, it's a userspace list!)
* and mark any locks found there dead, and notify any waiters.
*
@@ -1742,14 +1774,14 @@
{
struct robust_list_head __user *head = curr->robust_list;
struct robust_list __user *entry, *pending;
- unsigned int limit = ROBUST_LIST_LIMIT;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
unsigned long futex_offset;
/*
* Fetch the list head (which was registered earlier, via
* sys_set_robust_list()):
*/
- if (get_user(entry, &head->list.next))
+ if (fetch_robust_entry(&entry, &head->list.next, &pi))
return;
/*
* Fetch the relative futex offset:
@@ -1760,10 +1792,11 @@
* Fetch any possibly pending lock-add first, and handle it
* if it exists:
*/
- if (get_user(pending, &head->list_op_pending))
+ if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
return;
+
if (pending)
- handle_futex_death((void *)pending + futex_offset, curr);
+ handle_futex_death((void *)pending + futex_offset, curr, pip);
while (entry != &head->list) {
/*
@@ -1772,12 +1805,12 @@
*/
if (entry != pending)
if (handle_futex_death((void *)entry + futex_offset,
- curr))
+ curr, pi))
return;
/*
* Fetch the next entry in the list:
*/
- if (get_user(entry, &entry->next))
+ if (fetch_robust_entry(&entry, &entry->next, &pi))
return;
/*
* Avoid excessively long or circular lists:
