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| author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2014-11-18 09:30:01 +0100 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-01-06 20:02:52 +0100 |
| commit | abaf3f9d275b8d856ae5e47531e40c0bfeac012b (patch) | |
| tree | 017561fdbffe2f3e840d6af7c5a7bbcf015c70c9 /kernel/rcu/tree.h | |
| parent | rcu: Note quiescent state when CPU goes offline (diff) | |
| download | linux-abaf3f9d275b8d856ae5e47531e40c0bfeac012b.tar.xz linux-abaf3f9d275b8d856ae5e47531e40c0bfeac012b.zip | |
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>
Diffstat (limited to 'kernel/rcu/tree.h')
| -rw-r--r-- | kernel/rcu/tree.h | 5 |
1 files changed, 0 insertions, 5 deletions
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 883ebc8e2b6e..95356477d560 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -172,11 +172,6 @@ struct rcu_node { /* queued on this rcu_node structure that */ /* are blocking the current grace period, */ /* there can be no such task. */ - struct completion boost_completion; - /* Used to ensure that the rt_mutex used */ - /* to carry out the boosting is fully */ - /* released with no future boostee accesses */ - /* before that rt_mutex is re-initialized. */ struct rt_mutex boost_mtx; /* Used only for the priority-boosting */ /* side effect, not as a lock. */ |