GIT: unionfs2-2.6.27.y: ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages

[Erez Zadok]

commit 70635511aad7493f7748aa4e42dd852dfc0eb73f
Author: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
Date:   Fri May 28 14:27:23 2010 -0500

    ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages
    
    commit 2acf2c261b823d9d9ed954f348b97620297a36b5 upstream.
    
    With delayed allocation we lock the page in write_cache_pages() and
    try to build an in memory extent of contiguous blocks.  This is needed
    so that we can get large contiguous blocks request.  If range_cyclic
    mode is enabled, write_cache_pages() will loop back to the 0 index if
    no I/O has been done yet, and try to start writing from the beginning
    of the range.  That causes an attempt to take the page lock of lower
    index page while holding the page lock of higher index page, which can
    cause a dead lock with another writeback thread.
    
    The solution is to implement the range_cyclic behavior in
    ext4_da_writepages() instead.
    
    http://bugzilla.kernel.org/show_bug.cgi?id=12579
    
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
    Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
    Signed-off-by: Jayson R. King <dev at jaysonking.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 154bb60..536e392 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2575,6 +2575,7 @@ static int ext4_da_writepages(struct address_space *mapping,
 	struct mpage_da_data mpd;
 	struct inode *inode = mapping->host;
 	long pages_written = 0, pages_skipped;
+	int range_cyclic, cycled = 1, io_done = 0;
 	int needed_blocks, ret = 0, nr_to_writebump = 0;
 	struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
 
@@ -2612,9 +2613,15 @@ static int ext4_da_writepages(struct address_space *mapping,
 	if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 		range_whole = 1;
 
-	if (wbc->range_cyclic)
+	range_cyclic = wbc->range_cyclic;
+	if (wbc->range_cyclic) {
 		index = mapping->writeback_index;
-	else
+		if (index)
+			cycled = 0;
+		wbc->range_start = index << PAGE_CACHE_SHIFT;
+		wbc->range_end  = LLONG_MAX;
+		wbc->range_cyclic = 0;
+	} else
 		index = wbc->range_start >> PAGE_CACHE_SHIFT;
 
 	mpd.wbc = wbc;
@@ -2622,6 +2629,7 @@ static int ext4_da_writepages(struct address_space *mapping,
 
 	pages_skipped = wbc->pages_skipped;
 
+retry:
 	while (!ret && wbc->nr_to_write > 0) {
 
 		/*
@@ -2676,6 +2684,7 @@ static int ext4_da_writepages(struct address_space *mapping,
 			pages_written += mpd.pages_written;
 			wbc->pages_skipped = pages_skipped;
 			ret = 0;
+			io_done = 1;
 		} else if (wbc->nr_to_write)
 			/*
 			 * There is no more writeout needed
@@ -2684,6 +2693,13 @@ static int ext4_da_writepages(struct address_space *mapping,
 			 */
 			break;
 	}
+	if (!io_done && !cycled) {
+		cycled = 1;
+		index = 0;
+		wbc->range_start = index << PAGE_CACHE_SHIFT;
+		wbc->range_end  = mapping->writeback_index - 1;
+		goto retry;
+	}
 	if (pages_skipped != wbc->pages_skipped)
 		printk(KERN_EMERG "This should not happen leaving %s "
 				"with nr_to_write = %ld ret = %d\n",
@@ -2691,6 +2707,7 @@ static int ext4_da_writepages(struct address_space *mapping,
 
 	/* Update index */
 	index += pages_written;
+	wbc->range_cyclic = range_cyclic;
 	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
 		/*
 		 * set the writeback_index so that range_cyclic