misc/fsck.c: Processes may kill other processes.

misc/fsck.c: Processes may kill other processes.

I find a error in misc/fsck.c, if run the fsck -N command, processes
don't execute, just show what would be done. However, the pid whose
value is -1 is added to the instance_list list in the execute
function,if the kill_all function is called later, kill(-1, signum)
is executed, Signals are sent to all processes except the number one
process and itself. Other processes will be killed if they use the
default signal processing function.

Signed-off-by: zhanchengbin <zhanchengbin1@huawei.com>
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>