From c814b39cbd18becb8e8948f3788766adcee9bde9 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Sat, 23 Aug 2014 14:49:23 -0400
Subject: [PATCH] add patch fix-BUG_ON-in-mb_free_blocks

---
 fix-BUG_ON-in-mb_free_blocks | 59 ++++++++++++++++++++++++++++++++++++++++++++
 series                       |  1 +
 2 files changed, 60 insertions(+)
 create mode 100644 fix-BUG_ON-in-mb_free_blocks

diff --git a/fix-BUG_ON-in-mb_free_blocks b/fix-BUG_ON-in-mb_free_blocks
new file mode 100644
index 00000000..ad9cf8da
--- /dev/null
+++ b/fix-BUG_ON-in-mb_free_blocks
@@ -0,0 +1,59 @@
+ext4: fix BUG_ON in mb_free_blocks()
+
+If we suffer a block allocation failure (for example due to a memory
+allocation failure), it's possible that we will call
+ext4_discard_allocated_blocks() before we've actually allocated any
+blocks.  In that case, fe_len and fe_start in ac->ac_f_ex will still
+be zero, and this will result in mb_free_blocks(inode, e4b, 0, 0)
+triggering the BUG_ON on mb_free_blocks():
+
+	BUG_ON(last >= (sb->s_blocksize << 3));
+
+Fix this by bailing out of ext4_discard_allocated_blocks() if fs_len
+is zero.
+
+Also fix a missing ext4_mb_unload_buddy() call in
+ext4_discard_allocated_blocks().
+
+Google-Bug-Id: 16844242
+
+Fixes: 86f0afd463215fc3e58020493482faa4ac3a4d69
+Signed-off-by: Theodore Ts'o <tytso@mit.edu>
+Cc: stable@vger.kernel.org
+---
+ fs/ext4/mballoc.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
+index 9560277..8b0f9ef 100644
+--- a/fs/ext4/mballoc.c
++++ b/fs/ext4/mballoc.c
+@@ -1412,6 +1412,8 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
+ 	int last = first + count - 1;
+ 	struct super_block *sb = e4b->bd_sb;
+ 
++	if (WARN_ON(count == 0))
++		return;
+ 	BUG_ON(last >= (sb->s_blocksize << 3));
+ 	assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
+ 	/* Don't bother if the block group is corrupt. */
+@@ -3221,6 +3223,8 @@ static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
+ 	int err;
+ 
+ 	if (pa == NULL) {
++		if (ac->ac_f_ex.fe_len == 0)
++			return;
+ 		err = ext4_mb_load_buddy(ac->ac_sb, ac->ac_f_ex.fe_group, &e4b);
+ 		if (err) {
+ 			/*
+@@ -3235,6 +3239,7 @@ static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
+ 		mb_free_blocks(ac->ac_inode, &e4b, ac->ac_f_ex.fe_start,
+ 			       ac->ac_f_ex.fe_len);
+ 		ext4_unlock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
++		ext4_mb_unload_buddy(&e4b);
+ 		return;
+ 	}
+ 	if (pa->pa_type == MB_INODE_PA)
+-- 
+2.1.0
+
diff --git a/series b/series
index 6df23b69..1575700a 100644
--- a/series
+++ b/series
@@ -1,6 +1,7 @@
 # BASE v3.17-rc1
 
 propagate-errors-up-to-ext4_find_entry-s-callers
+fix-BUG_ON-in-mb_free_blocks
 
 ##########################################
 # unstable patches
-- 
2.11.4.GIT