From: Robin Dong <sanbai@taobao.com>
Date: Wed, 26 Oct 2011 09:14:27 +0000 (-0400)
Subject: ext4: use stream-alloc when mb_group_prealloc set to zero
X-Git-Tag: firefly_0821_release~3680^2~4229^2~29
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ebbe027797f67d34708ccfabdb129886d549f9ce;p=firefly-linux-kernel-4.4.55.git

ext4: use stream-alloc when mb_group_prealloc set to zero

The kernel will crash on

ext4_mb_mark_diskspace_used:
	BUG_ON(ac->ac_b_ex.fe_len <= 0);

after we set /sys/fs/ext4/sda/mb_group_prealloc to zero and create new files in an ext4 filesystem.

The reason is: ac_b_ex.fe_len also set to zero(mb_group_prealloc) in ext4_mb_normalize_group_request
because the ac_flags contains EXT4_MB_HINT_GROUP_ALLOC.

I think when someone set mb_group_prealloc to zero, it means DO NOT USE GROUP PREALLOCATION,
so we should set alloc-strategy to STREAM in this case.

Signed-off-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index cd70b3041185..89762652aae2 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4006,6 +4006,11 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
 		return;
 	}
 
+	if (sbi->s_mb_group_prealloc <= 0) {
+		ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
+		return;
+	}
+
 	/* don't use group allocation for large files */
 	size = max(size, isize);
 	if (size > sbi->s_mb_stream_request) {