euler inclusion
category: bugfix
bugzilla: 46858
CVE: NA

---------------------------

The present code doesn't support concurrency mode, test it this way will
cause kernel panic.

The reason is that 'buff_used' didn't use any concurrent access
mechanism.

Fix the problem by following changes:
1. move the initialization of buffer from proc_dpages_open to
seq_read_dirty.
2. use mutex for 'buff_used'.
3. before calling simple_read_from_buffer in seq_read_dirty, judge if
the buffer changed since last read. If so, return -EFAULT.
Signed-off-by: Nyu kuai <yukuai3@huawei.com>
Signed-off-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NDianfang Zhang <zhangdianfang@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>