futex: avoid wake_futex() for a PI futex_q (aa10990e) · Commits · 戴 / test

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>

kernel/futex.c

+17 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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