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Commit aa10990e authored by Darren Hart's avatar Darren Hart Committed by Linus Torvalds
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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: default avatarDarren Hart <dvhart@linux.intel.com>
Reported-by: default avatarDave 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8ffeb9b0

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 @@ futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, 


	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 @@ futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, 
		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 @@ futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, 
		ret += op_ret;

	}



out_unlock:

	double_unlock_hb(hb1, hb2);

out_put_keys:

	put_futex_key(&key2);
@@ -1387,9 +1399,13 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, 
		/*

		 * 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;

		}