linux-kernel - [tip:locking/core] workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes

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Date:   Wed, 25 Oct 2017 04:13:23 -0700
From:   tip-bot for Byungchul Park <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, tglx@...utronix.de, hpa@...or.com,
        torvalds@...ux-foundation.org, mingo@...nel.org,
        byungchul.park@....com, linux-kernel@...r.kernel.org
Subject: [tip:locking/core] workqueue: Remove now redundant lock
 acquisitions wrt. workqueue flushes

Commit-ID:  fd1a5b04dfb899f84ddeb8acdaea6b98283df1e5
Gitweb:     https://git.kernel.org/tip/fd1a5b04dfb899f84ddeb8acdaea6b98283df1e5
Author:     Byungchul Park <byungchul.park@....com>
AuthorDate: Wed, 25 Oct 2017 17:56:04 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 25 Oct 2017 12:19:03 +0200

workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes

The workqueue code added manual lock acquisition annotations to catch
deadlocks.

After lockdepcrossrelease was introduced, some of those became redundant,
since wait_for_completion() already does the acquisition and tracking.

Remove the duplicate annotations.

Signed-off-by: Byungchul Park <byungchul.park@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: amir73il@...il.com
Cc: axboe@...nel.dk
Cc: darrick.wong@...cle.com
Cc: david@...morbit.com
Cc: hch@...radead.org
Cc: idryomov@...il.com
Cc: johan@...nel.org
Cc: johannes.berg@...el.com
Cc: kernel-team@....com
Cc: linux-block@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-mm@...ck.org
Cc: linux-xfs@...r.kernel.org
Cc: oleg@...hat.com
Cc: tj@...nel.org
Link: http://lkml.kernel.org/r/1508921765-15396-9-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/workqueue.h |  4 ++--
 kernel/workqueue.c        | 19 +++----------------
 2 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 1c49431..c8a572c 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -218,7 +218,7 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
 									\
 		__init_work((_work), _onstack);				\
 		(_work)->data = (atomic_long_t) WORK_DATA_INIT();	\
-		lockdep_init_map(&(_work)->lockdep_map, #_work, &__key, 0); \
+		lockdep_init_map(&(_work)->lockdep_map, "(work_completion)"#_work, &__key, 0); \
 		INIT_LIST_HEAD(&(_work)->entry);			\
 		(_work)->func = (_func);				\
 	} while (0)
@@ -398,7 +398,7 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
 	static struct lock_class_key __key;				\
 	const char *__lock_name;					\
 									\
-	__lock_name = #fmt#args;					\
+	__lock_name = "(wq_completion)"#fmt#args;			\
 									\
 	__alloc_workqueue_key((fmt), (flags), (max_active),		\
 			      &__key, __lock_name, ##args);		\
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 39831b2..160fdc6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2497,15 +2497,8 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
 	INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
 	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
 
-	/*
-	 * Explicitly init the crosslock for wq_barrier::done, make its lock
-	 * key a subkey of the corresponding work. As a result we won't
-	 * build a dependency between wq_barrier::done and unrelated work.
-	 */
-	lockdep_init_map_crosslock((struct lockdep_map *)&barr->done.map,
-				   "(complete)wq_barr::done",
-				   target->lockdep_map.key, 1);
-	__init_completion(&barr->done);
+	init_completion_map(&barr->done, &target->lockdep_map);
+
 	barr->task = current;
 
 	/*
@@ -2611,16 +2604,13 @@ void flush_workqueue(struct workqueue_struct *wq)
 	struct wq_flusher this_flusher = {
 		.list = LIST_HEAD_INIT(this_flusher.list),
 		.flush_color = -1,
-		.done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
+		.done = COMPLETION_INITIALIZER_ONSTACK_MAP(this_flusher.done, wq->lockdep_map),
 	};
 	int next_color;
 
 	if (WARN_ON(!wq_online))
 		return;
 
-	lock_map_acquire(&wq->lockdep_map);
-	lock_map_release(&wq->lockdep_map);
-
 	mutex_lock(&wq->mutex);
 
 	/*
@@ -2883,9 +2873,6 @@ bool flush_work(struct work_struct *work)
 	if (WARN_ON(!wq_online))
 		return false;
 
-	lock_map_acquire(&work->lockdep_map);
-	lock_map_release(&work->lockdep_map);
-
 	if (start_flush_work(work, &barr)) {
 		wait_for_completion(&barr.done);
 		destroy_work_on_stack(&barr.work);