tracing: Set actual size after ring buffer resize

tracing: Set actual size after ring buffer resize

[ Upstream commit 6d98a0f2ac3c021d21be66fa34e992137cd25bcb ]

Currently we can resize trace ringbuffer by writing a value into file
'buffer_size_kb', then by reading the file, we get the value that is
usually what we wrote. However, this value may be not actual size of
trace ring buffer because of the round up when doing resize in kernel,
and the actual size would be more useful.

Link: https://lore.kernel.org/linux-trace-kernel/20230705002705.576633-1-zhengyejian1@huawei.com
Cc: <mhiramat@kernel.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Stable-dep-of: d78ab792705c ("tracing: Stop current tracer when resizing buffer")
Signed-off-by: Sasha Levin <sashal@kernel.org>