The following commit has been merged into the locking/urgent branch of tip:

Commit-ID: 12bb3f7f1b03d5913b3f9d4236a488aa7774dfe9 Gitweb: https://git.kernel.org/tip/12bb3f7f1b03d5913b3f9d4236a488aa7774dfe9 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Wed, 20 Jan 2021 16:00:24 +01:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Tue, 26 Jan 2021 15:10:58 +01:00

futex: Ensure the correct return value from futex_lock_pi()

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 --- kernel/futex.c | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c index c47d101..d5e61c2 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2373,8 +2373,8 @@ retry: }

if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) { - /* We got the lock after all, nothing to fix. */ - ret = 0; + /* We got the lock. pi_state is correct. Tell caller. */ + ret = 1; goto out_unlock; }

@@ -2402,7 +2402,7 @@ retry: * We raced against a concurrent self; things are * already fixed up. Nothing to do. */ - ret = 0; + ret = 1; goto out_unlock; } newowner = argowner; @@ -2448,7 +2448,7 @@ retry: raw_spin_unlock(&newowner->pi_lock); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);

- return 0; + return argowner == current;

/* * In order to reschedule or handle a page fault, we need to drop the @@ -2490,7 +2490,7 @@ handle_err: * Check if someone else fixed it for us: */ if (pi_state->owner != oldowner) { - ret = 0; + ret = argowner == current; goto out_unlock; }

@@ -2523,8 +2523,6 @@ static long futex_wait_restart(struct restart_block *restart); */ 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 @@ -2535,8 +2533,8 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) * stable state, anything else needs more attention. */ if (q->pi_state->owner != current) - ret = fixup_pi_state_owner(uaddr, q, current); - return ret ? ret : locked; + return fixup_pi_state_owner(uaddr, q, current); + return 1; }

/* @@ -2547,10 +2545,8 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) * 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); - return ret; - } + 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 @@ -2563,7 +2559,7 @@ static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) q->pi_state->owner); }

- return ret; + return 0; }

/** @@ -3261,7 +3257,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, if (q.pi_state && (q.pi_state->owner != current)) { spin_lock(q.lock_ptr); ret = fixup_pi_state_owner(uaddr2, &q, current); - if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { + if (ret < 0 && rt_mutex_owner(&q.pi_state->pi_mutex) == current) { pi_state = q.pi_state; get_pi_state(pi_state); } @@ -3271,6 +3267,11 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, */ 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;