diff mbox

[07/10] writeback: use unlocked_inode_to_wb transaction in inode_congested()

Message ID 1428351508-8399-8-git-send-email-tj@kernel.org (mailing list archive)
State New, archived
Headers show

Commit Message

Tejun Heo April 6, 2015, 8:18 p.m. UTC
Similar to wb stat updates, inode_congested() accesses the associated
wb of an inode locklessly, which will break with foreign inode wb
switching.  This path updates inode_congested() to use unlocked inode
wb access transaction introduced by the previous patch.

Combined with the previous two patches, this makes all wb list and
access operations to be protected by either of inode->i_lock,
wb->list_lock, or mapping->tree_lock while wb switching is in

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
 fs/fs-writeback.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)
diff mbox


diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 97fb7f3..ee65ff09 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -596,10 +596,18 @@  void wbc_account_io(struct writeback_control *wbc, struct page *page,
 int inode_congested(struct inode *inode, int cong_bits)
-	if (inode) {
-		struct bdi_writeback *wb = inode_to_wb(inode);
-		if (wb)
-			return wb_congested(wb, cong_bits);
+	/*
+	 * Once set, ->i_wb never becomes NULL while the inode is alive.
+	 * Start transaction iff ->i_wb is visible.
+	 */
+	if (inode && inode_to_wb(inode)) {
+		struct bdi_writeback *wb;
+		bool locked, congested;
+		wb = unlocked_inode_to_wb_begin(inode, &locked);
+		congested = wb_congested(wb, cong_bits);
+		unlocked_inode_to_wb_end(inode, locked);
+		return congested;
 	return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);