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A single fix for the futex code where an intermediate state in the

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underlying RT mutex was not handled correctly and triggering a BUG()
 instead of treating it as another variant of retry condition.
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Merge tag 'locking-urgent-2020-11-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull futex fix from Thomas Gleixner:
 "A single fix for the futex code where an intermediate state in the
  underlying RT mutex was not handled correctly and triggering a BUG()
  instead of treating it as another variant of retry condition"

* tag 'locking-urgent-2020-11-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Handle transient "ownerless" rtmutex state correctly
This commit is contained in:
Linus Torvalds 2020-11-08 09:56:37 -08:00
commit aaaaa7ecdc
1 changed files with 14 additions and 2 deletions
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16
kernel/futex.c
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@ -2380,10 +2380,22 @@ retry:
}
/*
* Since we just failed the trylock; there must be an owner.
* The trylock just failed, so either there is an owner or
* there is a higher priority waiter than this one.
*/
newowner = rt_mutex_owner(&pi_state->pi_mutex);
BUG_ON(!newowner);
/*
* If the higher priority waiter has not yet taken over the
* rtmutex then newowner is NULL. We can't return here with
* that state because it's inconsistent vs. the user space
* state. So drop the locks and try again. It's a valid
* situation and not any different from the other retry
* conditions.
*/
if (unlikely(!newowner)) {
err = -EAGAIN;
goto handle_err;
}
} else {
WARN_ON_ONCE(argowner != current);
if (oldowner == current) {