diff options
| author |   Thomas Gleixner <tglx@linutronix.de> | 2019-11-06 22:55:44 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2019-11-20 09:40:10 +0100 |
| commit | 3f186d974826847a07bc7964d79ec4eded475ad9 (patch) | |
| tree | 99bdae5f1dedc0f361465fae87165eea0598eab4 | |
| parent | futex: Provide state handling for exec() as well (diff) | |
| download | linux-dev-3f186d974826847a07bc7964d79ec4eded475ad9.tar.xz linux-dev-3f186d974826847a07bc7964d79ec4eded475ad9.zip | |
futex: Add mutex around futex exit
The mutex will be used in subsequent changes to replace the busy looping of
a waiter when the futex owner is currently executing the exit cleanup to
prevent a potential live lock.
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/20191106224556.845798895@linutronix.de
| -rw-r--r-- | include/linux/futex.h | 1 | ||||
| -rw-r--r-- | include/linux/sched.h | 1 | ||||
| -rw-r--r-- | kernel/futex.c | 16 |
3 files changed, 18 insertions, 0 deletions
diff --git a/include/linux/futex.h b/include/linux/futex.h index 9f2792427d64..5cc3fed27d4c 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -65,6 +65,7 @@ static inline void futex_init_task(struct task_struct *tsk) INIT_LIST_HEAD(&tsk->pi_state_list); tsk->pi_state_cache = NULL; tsk->futex_state = FUTEX_STATE_OK; + mutex_init(&tsk->futex_exit_mutex); } void futex_exit_recursive(struct task_struct *tsk); diff --git a/include/linux/sched.h b/include/linux/sched.h index 85dab2f721c9..1ebe540f8a08 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1053,6 +1053,7 @@ struct task_struct { #endif struct list_head pi_state_list; struct futex_pi_state *pi_state_cache; + struct mutex futex_exit_mutex; unsigned int futex_state; #endif #ifdef CONFIG_PERF_EVENTS diff --git a/kernel/futex.c b/kernel/futex.c index 0c9850af2724..46a81e611065 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3698,12 +3698,23 @@ static void futex_cleanup(struct task_struct *tsk) */ void futex_exit_recursive(struct task_struct *tsk) { + /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */ + if (tsk->futex_state == FUTEX_STATE_EXITING) + mutex_unlock(&tsk->futex_exit_mutex); tsk->futex_state = FUTEX_STATE_DEAD; } static void futex_cleanup_begin(struct task_struct *tsk) { /* + * Prevent various race issues against a concurrent incoming waiter + * including live locks by forcing the waiter to block on + * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in + * attach_to_pi_owner(). + */ + mutex_lock(&tsk->futex_exit_mutex); + + /* * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock. * * This ensures that all subsequent checks of tsk->futex_state in @@ -3726,6 +3737,11 @@ static void futex_cleanup_end(struct task_struct *tsk, int state) * take another loop until it becomes visible. */ tsk->futex_state = state; + /* + * Drop the exit protection. This unblocks waiters which observed + * FUTEX_STATE_EXITING to reevaluate the state. + */ + mutex_unlock(&tsk->futex_exit_mutex); } void futex_exec_release(struct task_struct *tsk) |