lkml.org 
[lkml]   [2017]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH tip/core/rcu 7/9] rcu: Pretend ->boost_mtx acquired legitimately
Date
RCU priority boosting uses rt_mutex_init_proxy_locked() to initialize an
rt_mutex structure in locked state held by some other task. When that
other task releases it, lockdep complains (quite accurately, but a bit
uselessly) that the other task never acquired it. This complaint can
suppress other, more helpful, lockdep complaints, and in any case it is
a false positive.

This commit therefore uses the mutex_acquire() macro to make it look
like that other process legitimately acquired the lock, thus suppressing
this lockdep false-positive complaint.

Of course, if lockdep ever learns about rt_mutex_init_proxy_locked(),
this commit will need to be reverted.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcu/tree_plugin.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fed95fa941e6..60bfb16c9a1a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -529,8 +529,11 @@ void rcu_read_unlock_special(struct task_struct *t)
}

/* Unboost if we were boosted. */
- if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
+ if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) {
+ /* For lockdep, pretend we acquired lock honestly. */
+ mutex_acquire(&rnp->boost_mtx.dep_map, 0, 0, _RET_IP_);
rt_mutex_unlock(&rnp->boost_mtx);
+ }

/*
* If this was the last task on the expedited lists,
--
2.5.2
\
 
 \ /
  Last update: 2017-10-04 23:32    [W:0.155 / U:0.576 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site