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From: David Sterba <dsterba@suse.com>
To: linux-btrfs@vger.kernel.org
Cc: David Sterba <dsterba@suse.com>
Subject: [PATCH 10/11] btrfs: dev-replace: remove custom read/write blocking scheme
Date: Fri,  7 Sep 2018 16:55:22 +0200	[thread overview]
Message-ID: <e3b6d57cfd31a91299596d517cdb04888e87bdfd.1536331604.git.dsterba@suse.com> (raw)
In-Reply-To: <cover.1536331604.git.dsterba@suse.com>

After the rw semaphore has been added, the custom blocking using
::blocking_readers and ::read_lock_wq is redundant.

The blocking logic in __btrfs_map_block is replaced by extending the
time the semaphore is held, that has the same blocking effect on writes
as the previous custom scheme that waited until ::blocking_readers was
zero.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/ctree.h       |  2 --
 fs/btrfs/dev-replace.c | 16 ----------------
 fs/btrfs/dev-replace.h |  1 -
 fs/btrfs/disk-io.c     |  2 --
 fs/btrfs/volumes.c     | 13 ++++++-------
 5 files changed, 6 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 02b5372a42d7..2a255d5897f8 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -367,8 +367,6 @@ struct btrfs_dev_replace {
 
 	struct mutex lock_finishing_cancel_unmount;
 	struct rw_semaphore rwsem;
-	atomic_t blocking_readers;
-	wait_queue_head_t read_lock_wq;
 
 	struct btrfs_scrub_progress scrub_progress;
 
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index ddaa9dcf8284..e8c2f418b2d7 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -965,14 +965,7 @@ void btrfs_dev_replace_read_unlock(struct btrfs_dev_replace *dev_replace)
 
 void btrfs_dev_replace_write_lock(struct btrfs_dev_replace *dev_replace)
 {
-again:
-	wait_event(dev_replace->read_lock_wq,
-		   atomic_read(&dev_replace->blocking_readers) == 0);
 	down_write(&dev_replace->rwsem);
-	if (atomic_read(&dev_replace->blocking_readers)) {
-		up_write(&dev_replace->rwsem);
-		goto again;
-	}
 }
 
 void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace)
@@ -980,15 +973,6 @@ void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace)
 	up_write(&dev_replace->rwsem);
 }
 
-/* inc blocking cnt and release read lock */
-void btrfs_dev_replace_set_lock_blocking(
-					struct btrfs_dev_replace *dev_replace)
-{
-	/* only set blocking for read lock */
-	atomic_inc(&dev_replace->blocking_readers);
-	up_read(&dev_replace->rwsem);
-}
-
 void btrfs_bio_counter_inc_noblocked(struct btrfs_fs_info *fs_info)
 {
 	percpu_counter_inc(&fs_info->dev_replace.bio_counter);
diff --git a/fs/btrfs/dev-replace.h b/fs/btrfs/dev-replace.h
index 795c551f5b5e..eec7289c2618 100644
--- a/fs/btrfs/dev-replace.h
+++ b/fs/btrfs/dev-replace.h
@@ -26,6 +26,5 @@ void btrfs_dev_replace_read_lock(struct btrfs_dev_replace *dev_replace);
 void btrfs_dev_replace_read_unlock(struct btrfs_dev_replace *dev_replace);
 void btrfs_dev_replace_write_lock(struct btrfs_dev_replace *dev_replace);
 void btrfs_dev_replace_write_unlock(struct btrfs_dev_replace *dev_replace);
-void btrfs_dev_replace_set_lock_blocking(struct btrfs_dev_replace *dev_replace);
 
 #endif
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3f73f2a3d67b..520b1d6f615f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2155,9 +2155,7 @@ static void btrfs_init_dev_replace_locks(struct btrfs_fs_info *fs_info)
 {
 	mutex_init(&fs_info->dev_replace.lock_finishing_cancel_unmount);
 	init_rwsem(&fs_info->dev_replace.rwsem);
-	atomic_set(&fs_info->dev_replace.blocking_readers, 0);
 	init_waitqueue_head(&fs_info->dev_replace.replace_wait);
-	init_waitqueue_head(&fs_info->dev_replace.read_lock_wq);
 }
 
 static void btrfs_init_qgroup(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 762a4499d00a..d1f83529ac80 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5706,10 +5706,12 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
 
 	btrfs_dev_replace_read_lock(dev_replace);
 	dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(dev_replace);
+	/*
+	 * Hold the semaphore for read during the whole operation, write is
+	 * requested at commit time but must wait.
+	 */
 	if (!dev_replace_is_ongoing)
 		btrfs_dev_replace_read_unlock(dev_replace);
-	else
-		btrfs_dev_replace_set_lock_blocking(dev_replace);
 
 	if (dev_replace_is_ongoing && mirror_num == map->num_stripes + 1 &&
 	    !need_full_stripe(op) && dev_replace->tgtdev != NULL) {
@@ -5904,11 +5906,8 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
 	}
 out:
 	if (dev_replace_is_ongoing) {
-		ASSERT(atomic_read(&dev_replace->blocking_readers) > 0);
-		btrfs_dev_replace_read_lock(dev_replace);
-		/* Barrier implied by atomic_dec_and_test */
-		if (atomic_dec_and_test(&dev_replace->blocking_readers))
-			cond_wake_up_nomb(&dev_replace->read_lock_wq);
+		lockdep_assert_held(&dev_replace->rwsem);
+		/* Unlock and let waiting writers proceed */
 		btrfs_dev_replace_read_unlock(dev_replace);
 	}
 	free_extent_map(em);
-- 
2.18.0

  parent reply	other threads:[~2018-09-07 19:36 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-07 14:54 [PATCH 00/11] Cleanup dev-replace locking David Sterba
2018-09-07 14:55 ` [PATCH 01/11] btrfs: remove btrfs_dev_replace::read_locks David Sterba
2018-09-07 14:55 ` [PATCH 02/11] btrfs: open code btrfs_dev_replace_clear_lock_blocking David Sterba
2018-09-07 14:55 ` [PATCH 03/11] btrfs: open code btrfs_dev_replace_stats_inc David Sterba
2018-09-07 21:02   ` Omar Sandoval
2018-09-07 14:55 ` [PATCH 04/11] btrfs: open code btrfs_after_dev_replace_commit David Sterba
2018-09-07 21:03   ` Omar Sandoval
2018-09-07 14:55 ` [PATCH 05/11] btrfs: dev-replace: avoid useless lock on error handling path David Sterba
2018-09-07 21:06   ` Omar Sandoval
2018-09-14 16:53   ` David Sterba
2018-09-07 14:55 ` [PATCH 06/11] btrfs: dev-replace: move replace members out of fs_info David Sterba
2018-09-07 21:09   ` Omar Sandoval
2018-09-07 14:55 ` [PATCH 07/11] btrfs: dev-replace: remove pointless assert in write unlock David Sterba
2018-09-07 14:55 ` [PATCH 08/11] btrfs: reada: reorder dev-replace locks before radix tree preload David Sterba
2018-09-07 14:55 ` [PATCH 09/11] btrfs: dev-replace: swich locking to rw semaphore David Sterba
2018-09-07 14:55 ` David Sterba [this message]
2018-09-07 14:55 ` [PATCH 11/11] btrfs: dev-replace: open code trivial locking helpers David Sterba
2018-09-27 11:06 ` [PATCH 00/11] Cleanup dev-replace locking David Sterba
2018-10-04  1:06   ` Anand Jain
2018-10-04 10:13     ` David Sterba
2018-10-05  8:58       ` Anand Jain

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