futex: avoid wake_futex() for a PI futex_q

Dave Jones reported a bug with futex_lock_pi() that his trinity test
exposed.  Sometime between queue_me() and taking the q.lock_ptr, the
lock_ptr became NULL, resulting in a crash.

While futex_wake() is careful to not call wake_futex() on futex_q's with
a pi_state or an rt_waiter (which are either waiting for a
futex_unlock_pi() or a PI futex_requeue()), futex_wake_op() and
futex_requeue() do not perform the same test.

Update futex_wake_op() and futex_requeue() to test for q.pi_state and
q.rt_waiter and abort with -EINVAL if detected.  To ensure any future
breakage is caught, add a WARN() to wake_futex() if the same condition
is true.

This fix has seen 3 hours of testing with "trinity -c futex" on an
x86_64 VM with 4 CPUS.

[akpm@linux-foundation.org: tidy up the WARN()]
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Reported-by: Dave Jones <davej@redat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: John Kacur <jkacur@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/futex.c b/kernel/futex.c
index 20ef219bbe9b76b3d54e6b501366f15cd97c464a..19eb089ca003a7f7a09347eb393d5241cc93342e 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -843,6 +843,9 @@ static void wake_futex(struct futex_q *q)
 {
        struct task_struct *p = q->task;
 
+       if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
+               return;
+
        /*
         * We set q->lock_ptr = NULL _before_ we wake up the task. If
         * a non-futex wake up happens on another CPU then the task
@@ -1078,6 +1081,10 @@ retry_private:
 
        plist_for_each_entry_safe(this, next, head, list) {
                if (match_futex (&this->key, &key1)) {
+                       if (this->pi_state || this->rt_waiter) {
+                               ret = -EINVAL;
+                               goto out_unlock;
+                       }
                        wake_futex(this);
                        if (++ret >= nr_wake)
                                break;
@@ -1090,6 +1097,10 @@ retry_private:
                op_ret = 0;
                plist_for_each_entry_safe(this, next, head, list) {
                        if (match_futex (&this->key, &key2)) {
+                               if (this->pi_state || this->rt_waiter) {
+                                       ret = -EINVAL;
+                                       goto out_unlock;
+                               }
                                wake_futex(this);
                                if (++op_ret >= nr_wake2)
                                        break;
@@ -1098,6 +1109,7 @@ retry_private:
                ret += op_ret;
        }
 
+out_unlock:
        double_unlock_hb(hb1, hb2);
 out_put_keys:
        put_futex_key(&key2);
@@ -1387,9 +1399,13 @@ retry_private:
                /*
                 * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
                 * be paired with each other and no other futex ops.
+                *
+                * We should never be requeueing a futex_q with a pi_state,
+                * which is awaiting a futex_unlock_pi().
                 */
                if ((requeue_pi && !this->rt_waiter) ||
-                   (!requeue_pi && this->rt_waiter)) {
+                   (!requeue_pi && this->rt_waiter) ||
+                   this->pi_state) {
                        ret = -EINVAL;
                        break;
                }