[ 3.5.y.z extended stable ] Patch "ext4: fix free clusters calculation in bigalloc filesystem" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Thu Feb 28 11:58:47 UTC 2013

This is a note to let you know that I have just added a patch titled

    ext4: fix free clusters calculation in bigalloc filesystem

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From b52b07bf48b4a96934d50303ad16f8dead0ba22c Mon Sep 17 00:00:00 2001
From: Lukas Czerner <lczerner at redhat.com>
Date: Fri, 22 Feb 2013 15:27:52 -0500
Subject: [PATCH] ext4: fix free clusters calculation in bigalloc filesystem

commit 304e220f0879198b1f5309ad6f0be862b4009491 upstream.

ext4_has_free_clusters() should tell us whether there is enough free
clusters to allocate, however number of free clusters in the file system
is converted to blocks using EXT4_C2B() which is not only wrong use of
the macro (we should have used EXT4_NUM_B2C) but it's also completely
wrong concept since everything else is in cluster units.

Moreover when calculating number of root clusters we should be using
macro EXT4_NUM_B2C() instead of EXT4_B2C() otherwise the result might be
off by one. However r_blocks_count should always be a multiple of the
cluster ratio so doing a plain bit shift should be enough here. We
avoid using EXT4_B2C() because it's confusing.

As a result of the first problem number of free clusters is much bigger
than it should have been and ext4_has_free_clusters() would return 1 even
if there is really not enough free clusters available.

Fix this by removing the EXT4_C2B() conversion of free clusters and
using bit shift when calculating number of root clusters. This bug
affects number of xfstests tests covering file system ENOSPC situation
handling. With this patch most of the ENOSPC problems with bigalloc file
system disappear, especially the errors caused by delayed allocation not
having enough space when the actual allocation is finally requested.

Signed-off-by: Lukas Czerner <lczerner at redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 fs/ext4/balloc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 33938c1..2f2e0da 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -484,11 +484,16 @@ static int ext4_has_free_clusters(struct ext4_sb_info *sbi,

 	free_clusters  = percpu_counter_read_positive(fcc);
 	dirty_clusters = percpu_counter_read_positive(dcc);
-	root_clusters = EXT4_B2C(sbi, ext4_r_blocks_count(sbi->s_es));
+	/*
+	 * r_blocks_count should always be multiple of the cluster ratio so
+	 * we are safe to do a plane bit shift only.
+	 */
+	root_clusters = ext4_r_blocks_count(sbi->s_es) >> sbi->s_cluster_bits;

 	if (free_clusters - (nclusters + root_clusters + dirty_clusters) <
-		free_clusters  = EXT4_C2B(sbi, percpu_counter_sum_positive(fcc));
+		free_clusters  = percpu_counter_sum_positive(fcc);
 		dirty_clusters = percpu_counter_sum_positive(dcc);
 	/* Check whether we have space after accounting for current

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