ftrace: Handle commands when closing set_ftrace_filter file

stable inclusion
from linux-4.19.191
commit 3d9281a4ac7171c808f9507f0937eb236b353905

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

commit 8c9af478 upstream.

 # echo switch_mm:traceoff > /sys/kernel/tracing/set_ftrace_filter

will cause switch_mm to stop tracing by the traceoff command.

 # echo -n switch_mm:traceoff > /sys/kernel/tracing/set_ftrace_filter

does nothing.

The reason is that the parsing in the write function only processes
commands if it finished parsing (there is white space written after the
command). That's to handle:

 write(fd, "switch_mm:", 10);
 write(fd, "traceoff", 8);

cases, where the command is broken over multiple writes.

The problem is if the file descriptor is closed, then the write call is
not processed, and the command needs to be processed in the release code.
The release code can handle matching of functions, but does not handle
commands.

Cc: stable@vger.kernel.org
Fixes: eda1e328 ("tracing: handle broken names in ftrace filter")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>