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futex: Sanitize exit state handling

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Instead of having a smp_mb() and an empty lock/unlock of task::pi_lock move
the state setting into to the lock section.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191106224556.645603214@linutronix.de
This commit is contained in:
Thomas Gleixner 2019-11-06 22:55:42 +01:00
parent 18f694385c
commit 4a8e991b91
1 changed files with 10 additions and 7 deletions
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17
kernel/futex.c
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@ -3703,16 +3703,19 @@ void futex_exit_recursive(struct task_struct *tsk)
void futex_exit_release(struct task_struct *tsk)
{
tsk->futex_state = FUTEX_STATE_EXITING;
/*
* Ensure that all new tsk->pi_lock acquisitions must observe
* FUTEX_STATE_EXITING. Serializes against attach_to_pi_owner().
*/
smp_mb();
/*
* Ensure that we must observe the pi_state in exit_pi_state_list().
* Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
*
* This ensures that all subsequent checks of tsk->futex_state in
* attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
* tsk->pi_lock held.
*
* It guarantees also that a pi_state which was queued right before
* the state change under tsk->pi_lock by a concurrent waiter must
* be observed in exit_pi_state_list().
*/
raw_spin_lock_irq(&tsk->pi_lock);
tsk->futex_state = FUTEX_STATE_EXITING;
raw_spin_unlock_irq(&tsk->pi_lock);
futex_exec_release(tsk);