[PATCH 3/7] block: use sb_for_each_inodes() in sync_bdevs()

[Julian Sun <sunjunchao@bytedance.com>]

Convert sync_bdevs() to sb_for_each_inodes() and move device writeback
into a callback. The iterator preserves the walk position, allowing the
callback to iput() its inode before reacquiring the list lock and removing
the old_inode reference carried across iterations.

Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
---
 block/bdev.c | 85 +++++++++++++++++++++++++---------------------------
 1 file changed, 41 insertions(+), 44 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index cd8323083740..ae472a062e51 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1336,56 +1336,53 @@ void bdev_mark_dead(struct block_device *bdev, bool surprise)
  */
 EXPORT_SYMBOL_GPL(bdev_mark_dead);
 
-void sync_bdevs(bool wait)
+static int sync_bdevs_inode_iter_cb(struct inode *inode, void *data)
 {
-	struct inode *inode, *old_inode = NULL;
-
-	spin_lock(&blockdev_superblock->s_inode_list_lock);
-	list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
-		struct address_space *mapping = inode->i_mapping;
-		struct block_device *bdev;
+	bool wait = (bool)data;
+	struct block_device *bdev;
+	struct address_space *mapping = inode->i_mapping;
 
-		spin_lock(&inode->i_lock);
-		if (inode_state_read(inode) & (I_FREEING | I_WILL_FREE | I_NEW) ||
-		    mapping->nrpages == 0) {
-			spin_unlock(&inode->i_lock);
-			continue;
-		}
-		__iget(inode);
+	if (mapping->nrpages == 0) {
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&blockdev_superblock->s_inode_list_lock);
+		return 0;
+	}
+
+	/*
+	 * We hold a reference to 'inode' so it couldn't have been
+	 * removed from s_inodes list while we dropped the
+	 * s_inode_list_lock.
+	 */
+	__iget(inode);
+	spin_unlock(&inode->i_lock);
+	spin_unlock(&blockdev_superblock->s_inode_list_lock);
+	bdev = I_BDEV(inode);
+
+	mutex_lock(&bdev->bd_disk->open_mutex);
+	if (!atomic_read(&bdev->bd_openers)) {
+		; /* skip */
+	} else if (wait) {
 		/*
-		 * We hold a reference to 'inode' so it couldn't have been
-		 * removed from s_inodes list while we dropped the
-		 * s_inode_list_lock  We cannot iput the inode now as we can
-		 * be holding the last reference and we cannot iput it under
-		 * s_inode_list_lock. So we keep the reference and iput it
-		 * later.
+		 * We keep the error status of individual mapping so
+		 * that applications can catch the writeback error using
+		 * fsync(2). See filemap_fdatawait_keep_errors() for
+		 * details.
 		 */
-		iput(old_inode);
-		old_inode = inode;
-		bdev = I_BDEV(inode);
-
-		mutex_lock(&bdev->bd_disk->open_mutex);
-		if (!atomic_read(&bdev->bd_openers)) {
-			; /* skip */
-		} else if (wait) {
-			/*
-			 * We keep the error status of individual mapping so
-			 * that applications can catch the writeback error using
-			 * fsync(2). See filemap_fdatawait_keep_errors() for
-			 * details.
-			 */
-			filemap_fdatawait_keep_errors(inode->i_mapping);
-		} else {
-			filemap_fdatawrite(inode->i_mapping);
-		}
-		mutex_unlock(&bdev->bd_disk->open_mutex);
-
-		spin_lock(&blockdev_superblock->s_inode_list_lock);
+		filemap_fdatawait_keep_errors(inode->i_mapping);
+	} else {
+		filemap_fdatawrite(inode->i_mapping);
 	}
-	spin_unlock(&blockdev_superblock->s_inode_list_lock);
-	iput(old_inode);
+	mutex_unlock(&bdev->bd_disk->open_mutex);
+	iput(inode);
+
+	spin_lock(&blockdev_superblock->s_inode_list_lock);
+
+	return 0;
+}
+
+void sync_bdevs(bool wait)
+{
+	sb_for_each_inodes(blockdev_superblock, INODE_ITER_NORMAL,
+			   sync_bdevs_inode_iter_cb, (void *)wait);
 }
 
 /*
-- 
2.39.5