linux-kernel - Re: [RFC] workqueue: Fix irq inversion deadlock in manage

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Message-ID: <20171009064257.43lfvc4ey7xrr7hz@hirez.programming.kicks-ass.net>
Date:   Mon, 9 Oct 2017 08:42:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org,
        Josef Bacik <josef@...icpanda.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [RFC] workqueue: Fix irq inversion deadlock in manage_workers()

On Sun, Oct 08, 2017 at 12:03:47PM -0700, Tejun Heo wrote:
> So, if I'm not mistaken, this is a regression caused by b9c16a0e1f73
> ("locking/mutex: Fix lockdep_assert_held() fail") which seems to
> replace irqsave operations inside mutex to unconditional irq ones.

No, it existed before that. You're looking at the DEBUG_MUTEX case, the
normal case looked like:

diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 4410a4af42a3..6ebc1902f779 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -9,10 +9,6 @@
  * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
  */
 
-#define spin_lock_mutex(lock, flags) \
-		do { spin_lock(lock); (void)(flags); } while (0)
-#define spin_unlock_mutex(lock, flags) \
-		do { spin_unlock(lock); (void)(flags); } while (0)
 #define mutex_remove_waiter(lock, waiter, task) \
 		__list_del((waiter)->list.prev, (waiter)->list.next)
 

Which is exactly what lives today.