[PATCH 4.9 13/49] futex: Ensure the correct return value from futex_lock_pi()

Greg Kroah-Hartman
2021-02-22T13:54:05Z

From: Thomas Gleixner <tglx@linutronix.de>

commit 12bb3f7f1b03d5913b3f9d4236a488aa7774dfe9 upstream

In case that futex_lock_pi() was aborted by a signal or a timeout and the
task returned without acquiring the rtmutex, but is the designated owner of
the futex due to a concurrent futex_unlock_pi() fixup_owner() is invoked to
establish consistent state. In that case it invokes fixup_pi_state_owner()
which in turn tries to acquire the rtmutex again. If that succeeds then it
does not propagate this success to fixup_owner() and futex_lock_pi()
returns -EINTR or -ETIMEOUT despite having the futex locked.

Return success from fixup_pi_state_owner() in all cases where the current
task owns the rtmutex and therefore the futex and propagate it correctly
through fixup_owner(). Fixup the other callsite which does not expect a
positive return value.

Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Lee: Back-ported in support of a previous futex attempt]
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/futex.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2322,7 +2322,7 @@ retry:
}

if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
- /* We got the lock after all, nothing to fix. */
+ /* We got the lock. pi_state is correct. Tell caller. */
return 1;
}

@@ -2364,7 +2364,7 @@ retry:
*/
pi_state_update_owner(pi_state, newowner);

- return 0;
+ return argowner == current;

/*
* To handle the page fault we need to drop the hash bucket
@@ -2447,8 +2447,6 @@ static long futex_wait_restart(struct re
*/
static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
{
- int ret = 0;
-
if (locked) {
/*
* Got the lock. We might not be the anticipated owner if we
@@ -2459,8 +2457,8 @@ static int fixup_owner(u32 __user *uaddr
* stable state, anything else needs more attention.
*/
if (q->pi_state->owner != current)
- ret = fixup_pi_state_owner(uaddr, q, current);
- goto out;
+ return fixup_pi_state_owner(uaddr, q, current);
+ return 1;
}

/*
@@ -2471,10 +2469,8 @@ static int fixup_owner(u32 __user *uaddr
* Another speculative read; pi_state->owner == current is unstable
* but needs our attention.
*/
- if (q->pi_state->owner == current) {
- ret = fixup_pi_state_owner(uaddr, q, NULL);
- goto out;
- }
+ if (q->pi_state->owner == current)
+ return fixup_pi_state_owner(uaddr, q, NULL);

/*
* Paranoia check. If we did not take the lock, then we should not be
@@ -2483,8 +2479,7 @@ static int fixup_owner(u32 __user *uaddr
if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
return fixup_pi_state_owner(uaddr, q, current);

-out:
- return ret ? ret : locked;
+ return 0;
}

/**
@@ -3106,6 +3101,11 @@ static int futex_wait_requeue_pi(u32 __u
*/
put_pi_state(q.pi_state);
spin_unlock(q.lock_ptr);
+ /*
+ * Adjust the return value. It's either -EFAULT or
+ * success (1) but the caller expects 0 for success.
+ */
+ ret = ret < 0 ? ret : 0;
}
} else {
struct rt_mutex *pi_mutex;