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| author | Thomas Gleixner <tglx@linutronix.de> | 2021-02-01 10:01:41 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-02-03 23:19:50 +0100 |
| commit | ad3466ae9d6d42c5918505d59aada8ad9f5be32a (patch) | |
| tree | af876724c89d45e58ada7bc6a8ba0a259127e98a /kernel | |
| parent | ff3a33f3c9d07b6def313562378ba39b76a73e7e (diff) | |
| download | linux-ad3466ae9d6d42c5918505d59aada8ad9f5be32a.tar.gz linux-ad3466ae9d6d42c5918505d59aada8ad9f5be32a.tar.bz2 linux-ad3466ae9d6d42c5918505d59aada8ad9f5be32a.zip | |
futex: Add mutex around futex exit
commit 3f186d974826847a07bc7964d79ec4eded475ad9 upstream.
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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/futex.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 50f61d0e51b5..e7798ef3b4b7 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3306,12 +3306,23 @@ 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 @@ -3334,6 +3345,11 @@ 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) |