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