linux-kernel - linux-next: manual merge of the block tree with the ext4 tree

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Date:	Thu, 27 Nov 2014 14:53:47 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Jens Axboe <axboe@...nel.dk>, Theodore Ts'o <tytso@....edu>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: linux-next: manual merge of the block tree with the ext4 tree

Hi Jens,

Today's linux-next merge of the block tree got a conflict in
fs/fs-writeback.c between commit ef7fdf5e8c87 ("vfs: add support for a
lazytime mount option") from the ext4 tree and commit 9c6ac78eb352
("writeback: fix a subtle race condition in I_DIRTY clearing") from the
block tree.

I fixed it up (I took a guess, plese check - see below) and can carry
the fix as necessary (no action is required).

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au

diff --cc fs/fs-writeback.c
index 3d87174408ae,2d609a5fbfea..000000000000
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@@ -482,14 -479,30 +482,30 @@@ __writeback_single_inode(struct inode *
  	 * write_inode()
  	 */
  	spin_lock(&inode->i_lock);
- 	/* Clear I_DIRTY_PAGES if we've written out all dirty pages */
- 	if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
- 		inode->i_state &= ~I_DIRTY_PAGES;
+ 
 -	dirty = inode->i_state & I_DIRTY;
 -	inode->i_state &= ~I_DIRTY;
 +	dirty = inode->i_state & I_DIRTY_INODE;
 +	inode->i_state &= ~I_DIRTY_INODE;
+ 
+ 	/*
+ 	 * Paired with smp_mb() in __mark_inode_dirty().  This allows
+ 	 * __mark_inode_dirty() to test i_state without grabbing i_lock -
+ 	 * either they see the I_DIRTY bits cleared or we see the dirtied
+ 	 * inode.
+ 	 *
+ 	 * I_DIRTY_PAGES is always cleared together above even if @mapping
+ 	 * still has dirty pages.  The flag is reinstated after smp_mb() if
+ 	 * necessary.  This guarantees that either __mark_inode_dirty()
+ 	 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
+ 	 */
+ 	smp_mb();
+ 
+ 	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+ 		inode->i_state |= I_DIRTY_PAGES;
+ 
  	spin_unlock(&inode->i_lock);
+ 
  	/* Don't write the inode if only I_DIRTY_PAGES was set */
 -	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
 +	if (dirty) {
  		int err = write_inode(inode, wbc);
  		if (ret == 0)
  			ret = err;

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