rcu: Revert "Allow post-unlock reference for rt_mutex" to avoid priority-inversion
The patch dfeb9765ce3c ("Allow post-unlock reference for rt_mutex")
ensured rcu-boost safe even the rt_mutex has post-unlock reference.
But rt_mutex allowing post-unlock reference is definitely a bug and it was
fixed by the commit 27e35715df54 ("rtmutex: Plug slow unlock race").
This fix made the previous patch (dfeb9765ce3c) useless.
And even worse, the priority-inversion introduced by the the previous
patch still exists.
rcu_read_unlock_special() {
rt_mutex_unlock(&rnp->boost_mtx);
/* Priority-Inversion:
* the current task had been deboosted and preempted as a low
* priority task immediately, it could wait long before reschedule in,
* and the rcu-booster also waits on this low priority task and sleeps.
* This priority-inversion makes rcu-booster can't work
* as expected.
*/
complete(&rnp->boost_completion);
}
Just revert the patch to avoid it.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2 files changed