Patch "writeback: Fix inode->i_io_list not be protected by inode->i_lock error" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    writeback: Fix inode->i_io_list not be protected by inode->i_lock error

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     writeback-fix-inode-i_io_list-not-be-protected-by-in.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a6d977e8d36035d60883d72a9a881a77520bfc03
Author: Jchao Sun <sunjunchao2870@xxxxxxxxx>
Date:   Tue May 24 08:05:40 2022 -0700

    writeback: Fix inode->i_io_list not be protected by inode->i_lock error
    
    [ Upstream commit 10e14073107dd0b6d97d9516a02845a8e501c2c9 ]
    
    Commit b35250c0816c ("writeback: Protect inode->i_io_list with
    inode->i_lock") made inode->i_io_list not only protected by
    wb->list_lock but also inode->i_lock, but inode_io_list_move_locked()
    was missed. Add lock there and also update comment describing
    things protected by inode->i_lock. This also fixes a race where
    __mark_inode_dirty() could move inode under flush worker's hands
    and thus sync(2) could miss writing some inodes.
    
    Fixes: b35250c0816c ("writeback: Protect inode->i_io_list with inode->i_lock")
    Link: https://lore.kernel.org/r/20220524150540.12552-1-sunjunchao2870@xxxxxxxxx
    CC: stable@xxxxxxxxxxxxxxx
    Signed-off-by: Jchao Sun <sunjunchao2870@xxxxxxxxx>
    Signed-off-by: Jan Kara <jack@xxxxxxx>
    Stable-dep-of: cbfecb927f42 ("fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 645e3f6ffe44..4c667662a4d9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -120,6 +120,7 @@ static bool inode_io_list_move_locked(struct inode *inode,
 				      struct list_head *head)
 {
 	assert_spin_locked(&wb->list_lock);
+	assert_spin_locked(&inode->i_lock);
 
 	list_move(&inode->i_io_list, head);
 
@@ -1282,9 +1283,9 @@ static int move_expired_inodes(struct list_head *delaying_queue,
 		inode = wb_inode(delaying_queue->prev);
 		if (inode_dirtied_after(inode, dirtied_before))
 			break;
+		spin_lock(&inode->i_lock);
 		list_move(&inode->i_io_list, &tmp);
 		moved++;
-		spin_lock(&inode->i_lock);
 		inode->i_state |= I_SYNC_QUEUED;
 		spin_unlock(&inode->i_lock);
 		if (sb_is_blkdev_sb(inode->i_sb))
@@ -1300,7 +1301,12 @@ static int move_expired_inodes(struct list_head *delaying_queue,
 		goto out;
 	}
 
-	/* Move inodes from one superblock together */
+	/*
+	 * Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
+	 * we don't take inode->i_lock here because it is just a pointless overhead.
+	 * Inode is already marked as I_SYNC_QUEUED so writeback list handling is
+	 * fully under our control.
+	 */
 	while (!list_empty(&tmp)) {
 		sb = wb_inode(tmp.prev)->i_sb;
 		list_for_each_prev_safe(pos, node, &tmp) {
@@ -1726,8 +1732,8 @@ static long writeback_sb_inodes(struct super_block *sb,
 			 * We'll have another go at writing back this inode
 			 * when we completed a full scan of b_io.
 			 */
-			spin_unlock(&inode->i_lock);
 			requeue_io(inode, wb);
+			spin_unlock(&inode->i_lock);
 			trace_writeback_sb_inodes_requeue(inode);
 			continue;
 		}
@@ -2265,6 +2271,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 {
 	struct super_block *sb = inode->i_sb;
 	int dirtytime = 0;
+	struct bdi_writeback *wb = NULL;
 
 	trace_writeback_mark_inode_dirty(inode, flags);
 
@@ -2316,6 +2323,17 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 			inode->i_state &= ~I_DIRTY_TIME;
 		inode->i_state |= flags;
 
+		/*
+		 * Grab inode's wb early because it requires dropping i_lock and we
+		 * need to make sure following checks happen atomically with dirty
+		 * list handling so that we don't move inodes under flush worker's
+		 * hands.
+		 */
+		if (!was_dirty) {
+			wb = locked_inode_to_wb_and_lock_list(inode);
+			spin_lock(&inode->i_lock);
+		}
+
 		/*
 		 * If the inode is queued for writeback by flush worker, just
 		 * update its dirty state. Once the flush worker is done with
@@ -2323,7 +2341,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		 * list, based upon its state.
 		 */
 		if (inode->i_state & I_SYNC_QUEUED)
-			goto out_unlock_inode;
+			goto out_unlock;
 
 		/*
 		 * Only add valid (hashed) inodes to the superblock's
@@ -2331,22 +2349,19 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		 */
 		if (!S_ISBLK(inode->i_mode)) {
 			if (inode_unhashed(inode))
-				goto out_unlock_inode;
+				goto out_unlock;
 		}
 		if (inode->i_state & I_FREEING)
-			goto out_unlock_inode;
+			goto out_unlock;
 
 		/*
 		 * If the inode was already on b_dirty/b_io/b_more_io, don't
 		 * reposition it (that would break b_dirty time-ordering).
 		 */
 		if (!was_dirty) {
-			struct bdi_writeback *wb;
 			struct list_head *dirty_list;
 			bool wakeup_bdi = false;
 
-			wb = locked_inode_to_wb_and_lock_list(inode);
-
 			inode->dirtied_when = jiffies;
 			if (dirtytime)
 				inode->dirtied_time_when = jiffies;
@@ -2360,6 +2375,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 							       dirty_list);
 
 			spin_unlock(&wb->list_lock);
+			spin_unlock(&inode->i_lock);
 			trace_writeback_dirty_inode_enqueue(inode);
 
 			/*
@@ -2374,6 +2390,9 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 			return;
 		}
 	}
+out_unlock:
+	if (wb)
+		spin_unlock(&wb->list_lock);
 out_unlock_inode:
 	spin_unlock(&inode->i_lock);
 }
diff --git a/fs/inode.c b/fs/inode.c
index 9f49e0bdc2f7..51726f2ad994 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -28,7 +28,7 @@
  * Inode locking rules:
  *
  * inode->i_lock protects:
- *   inode->i_state, inode->i_hash, __iget()
+ *   inode->i_state, inode->i_hash, __iget(), inode->i_io_list
  * Inode LRU list locks protect:
  *   inode->i_sb->s_inode_lru, inode->i_lru
  * inode->i_sb->s_inode_list_lock protects:



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